I've had the older Fermentasaurus for a while, but just got around to using it (on my second brew with it now).
In my opinion the pressure kit is mandatory; without it I'd just use a regular ported BMB like I do with my other brews, for easy gravity transfer.
With my first Fermetasaurs brew, I had the airlock on for a while until it started slowing; then added the pressure kit, because I didn't want the bulk of the fermentation under pressure. Once the kit is on there, you can immediately add bottle gas and purge the headspace if you are worried about it.
For this second brew, I just put the pressure kit on from the start and put an open ended hose from a gas disconnect running into a bottle of star san, just like a mini blowoff tube. That way I won't have to drop more stuff in there later, except for an oz of dry hops, and can easily swap the blowoff tube for a spunding valve at any time.
For this brew I want to cold crash, so that is why I used the Fermentasaurus. I know you can rig up O2 denying balloon setups with the BMB, but with the pressure kit, it will be super simple to just put a couple pounds of bottle gas pressure on to cold crash.