With an under-seat pack taking up most of my seat ...
358153
With an under-seat pack taking up most of my seat post and panniers on the back which obscure the seat stays, I needed a taillight that could be mounted on a horizontal rail which is part of the rear rack on my bike. This Serfas product fit the bill. The LEDs are very bright - visible even in daytime.
455216
Whatever this device would read, I would end up being slightly under when checking my bags.  At least it wasn't the other way around.
1980777
Needed a bag for my bike. It works really well, lots of room. My only problem is my seat is low, I cant really put too much heavy stuff in it. But thats just my bike.
4553119
I decided to replace the seats instead. It is a little late to ask to return them, So, I see if I can find someone who needs them.
1430663
I was kinda thinking that I would have some room for more clothing underneath this. I'm also not sure if I will need more clothing.
2593299
This backpack is not as comfortable as I had hoped.  The straps actually dig into my neck where they curve inwards at the top and do not sit comfortably on my shoulders when the pack is full.  The pack appears to be well made and there are lots of useful pockets.
3599304
It's a nice well made seat pack, but I wish I'd ordered the medium.  So many people were saying, "yeah, cell phone, tools, etc... no problem".  Maybe with the old small Apple phones, but my Galaxy S6 doesn't fit well at all, and it's not a big phone to today's standards. Once crammed in there, there is almost no room for anything else, like my wallet, let alone a spare tube, pri-bars, and a couple co2 bottles.

Will probably go ahead and buy the medium anyway, and give this one away to someone.  They really are well made packs, nice seat rail clamp, easy on/off, good zipper and materials.

edit... Bought the Medium size which fits things much better while not being that much larger of a pack.
538098
The size does not look like it will fit under the seat, I have flown Southwest and American with it and admittedly have not tried to get it under the seat for fear it will get stuck. However it fits overhead with enough room for my duffle bag to go Infront of it. I've used it three trips now and the seams are starting to stretch which is annoying since the bag is no where near full.
4593931
So so. It it a little too big around my seat belt, and I have to keep putting it in place. But it is soft.
4046998
I got two of these for our cars, because that is how it came up on the search.  They are probably a little big for the car, not fitting easily under the seat.  I haven't had to use it yet, thankfully, but its a trusted brand and a decent price.
203501
Fairly comfortable though the cushion at the waist pushes into my back to far.  Generous new and size of pockets, however only one has an inner pocket; I'd prefer a backpack with more inner pockets to separate items.  Also, the zippers are beginning to stick occasionally,  and I've had the pack for less than 3 months.
2131373
I am not tremendously large, but have found that for some reason on occasion I get a seat with a very small seat belt. This makes for a very uncomfortable flight. I have asked for the extender in the past and it always seemed to be a hassle for the attendant......if they even had one. Now I can simply use my own and not bother anyone.
4385757
Kept me from over packing as usual. First trip in years I was well under the required weight.
1647849
I spend a lot of time on the car and its nice to have a bit of organized space vs. filling up  the passenger seat
2024902
It's ok, I'm thinking of putting my stock seat back on as the front of the seat is cushion instead of leg clearance for peddling...
180554
I find the padding in this short not enough but at the same time my bike's seat is super hard also. I have used it once so still figuring this out, but I think I can recommend this to friends.
1516458
Had me on the edge of my.....well, I mostly read this lying down, so I can't say "seat," but I nearly fell off my bed a couple of times!