One thing about bikepacking is that there is no golden rule so, you have to make it work for you! Some people prefer having small front and rear panniers on their bikes, while others prefer fitting bikepacking bags in different places around the bike.
Bikepacking bags also include handlebar bags, top tube bags, feed bags, framepacks (top tube or full frame) and saddle seat packs such as the Lomo 13L bikepacking bag, which is a roll top and dry bag. In terms of weight distribution, the framepack wins over the other bikepacks because a framepack is fitted inside the triangle frame of the bike. The weight of the framepack is central over the bike so, the weight interferes very little with your handling of the bike.
The main drawback with the framepack though, it's its location, which is inside the triangle frame of the bike where the water bottle cage is also fitted. If the bike has a small triangle frame, you may not be able to accommodate a framepack and water bottle unless you mount the water bottle cage elsewhere on the bike like on the front fork of the bike. With a full framepack though, you can use a water bladder instead.
Even if the bike has a large triangle frame, having a top tube framepack above the water bottle cage will make a tight squeeze when reaching for the water bottle; hence you will have to replace the standard water bottle cage with a side entry water bottle cage.
The benefit of a seatpack such as the Lomo bikepacking seat pack is that you can fit large volume items in it. The main drawback though, it's the weight distribution. Because the seatpack sits high up on the bike, it will affect the balancing more than a framepack.
If you store a lot of heavy items inside a seatpack, it will swing around more, making it harder to corner on the bike. Realistically, you only want to store in the Lomo seatpack bulky, lightweight items like a rain jacket or sleeping bag.
The roll top design of the Lomo bikepacking seat pack is similar to the Lomo waterproof daysack, which is made of a thicker denier than the seat pack. Roll top bags make it super quick to undo the bag and take stuff out. The roll top seat pack also has the benefit of allowing you to roll up the bag down to compress the contents so, they don't shift inside the bag while riding.
To prevent the seat pack from swinging excessively, you do have to pack it really well by making sure the contents are stuffed right to the bottom of the seat pack. Unlike the other style of bikepacks, the bikepacking seat pack design has a corner-type base, which is needed in order to make contact with the seatpost of the bike. Most bike seat posts are rounded, although some seatposts (aero type) have a square tubular stem body, which is ideal for seat packs because it stops the bag from swinging as much.
Whether you have an aero seat post or not, you will have to tighten the seat pack velcro straps after riding the bike for a while because they will loosen up. To get good leverage when tightening up the velcro straps around the saddle, it's to wedge your knee in between the back of the seat pack and the tire to help you push the contents of the seat pack up into the saddle.
Another advantage you get with a seat pack versus a framepack is that a seat pack doubles as a handy mud guard. The Lomo bikepacking roll top seat pack is also a dry bag made of TPU waterproof material that, not only prevents water ingress but also makes the Lomo bikepacking seat pack easier to clean.
On the tail end of the seat pack, there is small rubber fabric loophole designed to clip a tail light, although you could also clip on other lightweight things like a bike helmet.
The 13 liter Lomo roll top saddle bag has a 52cm closed/rolled length with a 20cm height and 25cm maximum width expansion. The mouth of the bag measures 30cm long and has an approximate 24cm diameter.
The 13 liter Lomo seat pack is actually longer (65cm) but because of the short length of the buckle straps, you have to roll the top down a few times to clip the buckle straps, which are all sewn to the fabric of the bag via rubber fabric trims. The seams of the bag are joined together, using radio frequency (RF) welding. When empty, the total weight of the Lomo 13L bikepacking bag is 410 grams.
There are a total of four buckle straps and two large velcro straps with thick webbing, which provide a snug tight fit on the saddle's seat post. When clipped, the saddle buckle strap webbing measures 34cm long, while the roll top buckle strap webbing measures 21 cm long.
The velcro webbing straps measure 20cm long. The buckle straps feature elastic webbing keepers to manage the excess webbing. The roll top integrates female buckles, which are sewn to the mouth of the roll top via TPU strips, as well as a stiffener strip along the rim to help rolling up the excess material.
The Lomo seat pack is, mostly, a soft shell bag but, it does integrate plate stiffeners on the bottom sides (18cm long) and bottom base (32cm long) that provides enough structural integrity and a solid contact surface to allow the seat pack to remain upright against the seat post. There is also a large patch on the bottom base of the bag, which is made of the same type of rubber fabric found around the webbing strap seams.
Under bike seat storage and handlebar bags are the largest types of bags you can get for bikepacking, giving you the largest volume capacity. Bikepacking handle bags typically have dual openings to access contents at both ends.
Seat packs, however, are top loading so, they can only be accessed via one end, making it  not as convenient as a handlebar bag. With a seat pack, you have to be mindful of the order in which you pack things. For example, you wouldn't want to put items at the bottom of a seat pack that you may need at a pinch like bogroll or rain jacket.
Whichever type of bikepacking bag you use, the weight of the bikepacking bag will affect the handling of the bike. One last thing to consider before fitting any bikepack, it's that the velcro straps that secure the bikepack to the frame of the bike will move around a bit and may scuff the paint; hence it's a good idea putting protective tape on before fastening the velcro straps. You can buy the Lomo 13L saddle bag on amazon