The big difference between the two mic pres you mention has to do with the design.
The MPA . . . and anything by ART for that matter, is a typical transformerless, starved plate tube design. Basically a fancier version of the Tube MP. Nothing new or interesting there, other than the fact that you might like it's sound and functionality -- and quite a few people do, so I'm not really bashing it. As far as the starved plate stuff goes, it may be the best out there.
The Bellari, on the other hand, is at least an attempt to to make a tube mic pre with a design that's faithful to how real tube gear has traditionally been made. It has a distinct sound and vibe to it that the transformer front end and tube stage impart. This is not by any stretch to say that it's "hi fi" or upper crust gear, mind you.

It's still pretty cheap stuff, but it does at least offer a type of sound that isn't very common with any of the other cheapo tube or chip-based stuff out there.
Just recently, in fact, I had a fortunate accident with
the RP-220. I previously had it set up to record a very quiet singer. When the next singer stepped up to it, I forgot to adjust it -- and he was a very loud, aggressive type. As I'm sure you can guess, it was distorting and clipping every which way. Before I got a chance to turn it back down, everyone in the room marveled at how perfect the distortion was for that particular song, so I didn't touch it.
It can be a cool and fun toy to have around.