Got the 5.3L size for my Topstone XL, and it fits perfectly. Only used it on a few rides so far, but it has great build quality and lots of room for tools, water, snacks, clothing.
The large fit my 59 cm Warbird perfectly, great amount of space for everything you need for a full day on the roadtrail. I have ridden with it in some strong rain and everything inside stays perfectly dry. I would highly recommend this to anyone looking for a great half frame bag.
This bag has become one of my go-to bags. It is really well-made, stiff enough not to bulge out when full, waterproof, split compartments, zippers on both sides, and attaches with no sway. It fits the space on my gravel bike perfectly too (get the measurements from Apidura's web site). When out on a day ride, I can put my wallet, keys, covid mask and phone on the narrower side of the interior division. And I put an extra jacket, food, glasses, tire kit, etc. in the larger part.
This bag has become a mainstay for my longer rides, not just for bikepacking. When the weather is changeable, and I might need to carry an extra pair of gloves or jacket, this bag is perfect to take everything along. It's split into two zippered sections, so I use one for clothing, and the other for phone, keys, etc. The Apidura site lists all the bikes and frame sizes around, so you can make sure it fits. Excellent bag.
I am touring cross country and during the day most of my load is packed away in panniers. I use the frame pack for easy access to tire repair supplies and also for snacks, sunglasses, small items I want during the day. I have a handlebar that allows for multi hand positions and a handlebar bag does not fit. The frame pack is a great alternative!