Quite why this exists is something of a mystery, but I'm glad it does because without it, I wouldn't be writing this tripe for you lovely people to read.
First though, lets look at the bad things. For starters, there's no analogue stick here. If the R&D team (ha!) at XG - the manufacturer - had really thought about what they were doing, they could have modelled the pad after the Dual Shock and brought the world a dual analogue Dreamcast pad. Instead, they just knocked off the moulds for the original PS1 controller, left out any mention of analogue control (including the triggers), ignored the VMU slot and just placed a PCB inside a translucent case and added a couple of turbo buttons. Oh, and put a red LED in for good measure. Indeed, as with some other official peripherals, you must plug a VMU into a device in slot B in order to save and load your data. No biggie, but if the Treamcast mouse could have a handy VMU slot on the end of the wire, why couldn't this? And those stupidly expensive Ascii pads have VMU ports too, for that matter. It's a minor gripe, but we like to be thorough (nerdy) here at the 'Yard.
Oddly, the Game Heaven does feature two shoulder buttons (L1, L2 & R1, R2) and as mentioned previously they are strictly digital. I did play Sega Rally with the pad and even though they aren't analogue it doesn't really make much of a difference. The weird part is that L2 does the same as the B button and R2 does the same as X...which leads me to conclude that the Game Heaven was probably conceived for use with the multitude of 2D fighters on the Dreamcast. The turbo buttons (rather amusingly labelled TurBoY, TurBoX etc) also add weight to my hypothesis. The games I tried it with included KOF 2001, KOF '99, JoJo's, and Capcom Vs SNK...and it performed brilliantly with them all - the added diagonal sections of the D-pad do make a lot of difference when you're trying to unleash one of Terry Bogarde's special moves (he's the only character I can use in KOF because I'm shite, incidentally). I can imagine these extra degrees of control would make even more of a difference to somebody with something approaching 'skill' when it comes to 2D fighters, but even I could see the benefit. Yes, you could just use an arcade stick...but this is about the Game Heaven, m'kay.
Update: I've just realised I made no mention of trying this thing out with Bleemcast. There are plenty of PS1 games that make use of both the shoulder buttons and the Dreamcast controller cannot replicate this with its singular triggers. Whether PS1 games/Bleemcast will recognise the extra triggers on the Game Heaven is an interesting thought, as some games (such as the brilliant Mobil 1 Rally Championship) are not playable without them. Further investigation coming soon...