Several people have mentioned to me that like shooting infrared films on particularly the TLR's because they can leave the filter in place but still be able to compose and focus with the taking lens. Not having to remove, focus, and refit the filter for every shot is really handy! Nice tip! I've got a stockpile of infrared film just waiting for a bit of time to go shoot it, and maybe I'll take my TLR with me now. :-)
But IR filters in Bay IV mounts have been hard to get lately (DHW does stock other bay IV filters), so there are a couple solutions. The Rolleiflex filter adapter is one and quite handy, but also a bit expensive. But there are aftermarket Bay IV to filter adapters that might be worth checking out. See this link to an ebay vendor - that I have no connection with btw - but they look good. That way you can fit many different types of filters including the IR filter with the cutoff frequency you need.