The 6 gallon I ordered from HBS just came in today. I'll use it tomorrow. I also have a 3rd BMB coming soon. Initial impression of the fermonster are very good. I also still have one of my Better Bottles. Some initial impressions between the three are:
Fermonster:
Pros:
Smooth sides so cleaning could be easier than the Better Bottle and BMB.
No lid to modify for a good seal.
Same size bungs for the Better Bottles can be used with these fermenters.
Punted bottom seems to be higher than the BB and BMB.
Smaller in height, so probably better choice for smaller ferm chambers.
Cons:
Brew Hauler harness doesn't stay up due to the smooth sides (minor complaint).
Only two volume markings on the carboy at 5 and 6 gallons. Again, minor complaint.
Carboy's mouth is smaller than the BMB, so getting your hand down to the very bottom could be problematic.
About the same width as the Better Bottles, so could be crammed for space compared to the taller BMBs.
Big Mouth Bubbler:
Pros:
Large opening seems to be best for getting to the bottom for adequate cleaning.
Volume markings at every gallon.
Ribbed design seems to keep brew hauler snug in place.
dual ported lid availability.
Slimmer in width for better room in a ferm chamber.
Cons
Taller height may be problematic for smaller ferm chambers
Lids (gasket based and screw on) do not hold a good seal. Requires modding for the OCD brewer.
Requires a smaller bung due to the lid design.
Carboy seems thinner and "flexes" a bit easier than the Fermonster and BB.
Price is a bit on the high end, especially after all the accessories.
Lots of "nooks and crannies" in the BMB with the molded rib and bubble design in the plastic make it a bit harder to clean.
Better Bottle:
Pros:
Small neck best for the least amount of head space.
Uses same size bung as Fermonster.
Ribbed design makes it a bit more robust than the BMB, less flexing.
Ribbed design also seems to better suit use of a Brew Hauler harness or similar.
No lid sealing issues since a bung and airlock are all that's used.
Smaller height may be better suited for smaller ferm chambers.
Cons
When fully loaded, picking up the carboy will have some suck back unless you have these in a milk crate* (I don't have this issue with the BMB and the Fermonster is unknown at this time).
No volume markings, unless you know which ribs on the carboy tell you the amounts (1,3,5 I think).
Wider diameter may be problematic for some smaller ferm chambers.
Bung sized opening makes cleaning them a major PITA.
* I had issues with my BBs flexing to where sanitizer would suck back into the wort when picked up. Of course, the easy solution is a solid stopper until you get the carboy to its final destination. I never had this issue with my BMBs, but I use a solid stopper anyways and will do the same on all my fermenters.
Looking forward to seeing how this new fermenter stacks up. So far I'm liking what I'm seeing with it.