Other than a purely cosmetic standpoint ( less cables and not having to use a plug socket for the ONT) there is very little to be gained. Its not going to increase throughput or decrease latency. The Calix’s are decent units, and believe provide management and telemetry.
A very grey area is if you cause disruption for potentially up to 32 of your neighbours on the same pon, are you liable? I’ve not seen anything official anywhere from CF to say it’s not allowed. But I also wouldnt want to go up against CF’s legal team if it were to cause disruption.
Without seeing something official from CF to say yes go ahead and use an SFP ONU - heres a compatible list, then personally the potential cons outweigh the pros - but each to their own.
I’ll wait for the ISPreview news article of the user who took down their street for a couple of days 
