Do it, I've yet to do it myself but am still excited to give it a go. It isn't a good alternative to a 3 speed IGH though because it does add back to the bike not only a front derailleur but also a rear one (or a tensioner) so it's certainly less reliable than an IGH.The owner says it feels so much better than another he has with 3 in the hub. I might have to revise plans for my woods bike, this is so wrong it's right. With everyone in modern mountain biking currently hating on front derailleurs, I could see it giving my middle finger a little bit of rest
The positive though is that unlike with an IGH, should something fail its external, visible and therefore quite fixable. But I can't imagine the shifting experience being any better than an IGH which literally is instantaneous and quiet. Also far bigger risk of snapping or dropping the chain, if you go for big jumps. So I'd choose a really gradual jumps rather than massive hops.
If you don't want to use a rear derailleur as tensioner get an Alfine 2 pulley tensioner as that one is designed for multispeed up front combined with alfine 8 or 11. Else get a sexy old road derailleur designed for those 3 speed clusters.