The download page here shows links for 32-bit and 64-bit versions. I saw a post in the mfg.’s forum about a problem accessing an Access dB through a 64-bit installation; the Access headers differ according to bit-ness. (The problem was caused by FlowHeader x64 on a 64-bit OS with 32-bit Office installed.)
The response said you can install both the 32-bit and 64-bit versions on the same system. I installed and registered the x64 version first, before reading the forum post. I then installed the 32-bit version; it was already activated when I first ran it. Both versions appear to share both the license key and the option to search for new versions (I disabled it in the x64 version, and the same setting was reflected in the x32 version).