The Mono M80 I had ordered arrived today, and as promised here are some initial observations.
Overall, this is a well-designed gig bag, and I'd give it a preliminary rating of 4.5/5. Rating it in various categories, here are some scores (again, these are based on limited experience, I may feel differently after more time with the bag).
Protection: 4/5. I tested the bag with both of my basses (Rick 4003 and 4004Ci) and they both fit well. I believe the M80 will protect against all but heavy blows or significant weight being placed on it. The headlock system and the padding around the bottom strap button are good design features that provide extra protection. Dumping a glass of water on it showed it to be water-resistant at least; I won't take a hose to it (someone else can do those tests if they like) but I am confident it would be fine if spilled on or subject to a bit of rain. If I had to gate check it the bass would probably be fine, though I don't like gate-checking anything, even in a hard case. The materials and construction appear to be of good quality and likely to hold up well to the wear of use.
Mobility and transport: 4.5/5. The bag is a little bulkier than some because of its extra padding, but I don't think that's likely to matter in practice (and the extra inch or two of width is easy to accept given the protection). It's much easier to fit into a sedan trunk than a hard case, and should fit into standard airline overhead bins easily enough. The handle is comfortable and and bag balances well with a bass inside. The shoulder straps are reasonably comfortable and can be tucked away when not in use. When they were set on their lowest setting I was able to walk through doorways without ducking to keep from hitting the bass (I'm 6 feet tall, for reference). The weight is not bad at all, and this would be much more pleasant to schlep though an airport than a hard case.
Storage: 5/5. The main storage pocket has quite a lot of room--easily enough for cables, a couple pedals w/ power supplies, and a few other things. Adding the optional Tick accessory would provide a huge amount of storage, though it would also add to the cost.
Value: 3/5. While the cost ($170) wasn't out of line for this tier of gig bag quality, it certainly stings a bit, especially when I already have hard cases that provide more protection for my bass. However, it seems that this is the price of a good gig bag, based on the other options on the market. Still, I wonder if Mono could do better if they cut their prices a bit in a bit to move more units and boost their market share.
Overall, this is a good gig bag that provides a lot of protection and storage while remaining light and portable. I think the protection, design and materials are a significant step up from the usual Fender (what my local shop stocks) or Protec (what I've used in the past) or similar gig bags. The price reflects that, but it's probably worth it if you sometimes want to carry an expensive bass in a gig bag instead of a hard case.