Yes, the Dual Extruder V3.1 should work with your TAZ 6. As the description suggests, contact LulzBot support with your serial number to make sure.
I’ve had pretty good luck with mine when printing dual colors, not so much with water-soluble support material. More fine tuning would probably help but I haven’t spent the time.
I had some heat creep issues with the original V3 which should be better with the V3.1 but I went a slightly different route. See https://forum.lulzbot.com/t/repeated-fails-t6-dual-extruder-recently/23262.