I dunno about where you live but mid bmx bearings are about as common as it gets, just trying to help it is what i used to get some extra clearance. I think you miss understood about what i said about the idler, when you start having to pedal up hill the idler works a lot harder and you want it to stay as smooth as and not to be losing any watts. I found the cog idlers better in this regard, but hey only giving my opinion based on my experience :noidea:
In Europe they are not so common, at least at small bike shops, small towns with bikeparks and so on. Maybe BMX racing is more popular in AU? Here not so much. Clearance is not so big a deal, because I can always place a shock toward the non drive side. Problem is with tire clearance sideways and crankarm/cs interference, but simple bending will work like charm.
Those idlers are nice, but from my experience cog idlers are quite noisy and require different materials and sooooooo much more machining, to gain what 1-2% top? It is 150mm bike, even with so much anti squat it won't pedal like a roadbike so it is kinda pointless (in my opinion ofc). In my opinion idler diameter is far more important then if it is a cog shaped idler or a "regular" one.
Another thing is, that those idlers You were talking about are simply too big for me and 9t cog would be just terrible.
