Tribike Size

If you're 6-2 then it's doubtful a 56 cm frame would fit you properly and I would pass on it-

There's a whole lot of "it depends" in the answer to this.  I' m 6'3" with alligator arms and praying mantis legs, so my sizing always runs small for my height (I ride a medium Ridley road bike and a large Planet X tri bike...typically you would think I'd be looking at XL/58+ CM).

Is that 58 based on a rough calculator or an actual fitting recommendation?

I've always leaned towards having a bike that's too small rather than one that's two big.  You can easily mess with stem length, bar position, and seat height to stretch out a bike that's a little too small, but you can't shorten a top tube if it's too long.  Any way you can see it in person?

There is really no way to know if a bike will fit from the frame size alone.  Different brands will have a different stack, reach dimensions for the same frame size, and what fits in one brand may not fit in another.