I've used both the JMP and the BVM setup (and also the BVM puffer pipe with the JMP in-flight mixture) and all three of these combos work well. Personally, I prefer the BVM puffer pipe (though you have the added minor hassle of routing a length of fuel tubing into the duct) for simple reasons of cleanup.

The tanks will expand under pressure from both the pressure vent and the puffer pipe. If you roll inverted and pull back on the throttle (for instance when at the top of a Split-S), the fuel will enter the vent line and be exhausted from the vent/puffer. The puffer is much closer to the rear of the duct and aft of the engine so the majority of the fuel will be expelled without getting all over the inside of the duct and around the engine.

As for the length of tuned pipe, I would agree that the best course of action is to get a fixed length pipe. Two piece pipes with headers and couplers are a pain and they tend to come apart. BVM no longer makes pipes as they seem to be strictly supporting electric and turbine power, but you do run across them from time to time. JMP still seems to still make all the required pieces and they certainly do have a really great adaptor for the OS91 and a strong pipe hanger.

Good luck,

Jim