Do it! Tandems are so much fun.
I’ve ridden MTB tandems for many (20?) years now, starting with a Dawes Double Edge with cantis, then a front disc, then full discs and bought a 26in Cannondale tandem three or four years ago. Just so much fun.
I’m happy on the front or back, but I tend to be put on the front. The quality of DH and Enduro components now means that upgrading bikes to decent brakes and forks is pretty easy – and Guy Kesteven has a full 1×11 setup on his, which I might look into doing.
However, any mountain bike tandem is great fun and they’re surprisingly capable, both up and down. I did many Polaris events on mine (yes, that was us) and still enjoy getting ours out on local trails when things need spicing up…
Is it time we arranged another STW tandem gathering? Next, er, May perhaps? (Other months are available…)