First of all, there's not such thing as an "entry-level" vs. a "serious" FFM, they either do the job of they don't ... and then there's some variation. Any "tech" diver who, on the strength of only having used the Mantis, is telling you that it's what you need, is, I fear, a "tech" diver who is speaking from sheer ignorance driven by having misspend a fair piece of change on a Mantis.
Yes I have used both the Aquacom and the BuddyPhone. The Aquacom worked well, at short range it approached the quality of wired comms, the BuddyPhone, however, was often unintelligible.