I bought a TY91 transceiver and TT21 transponder about 10 years ago, since then i've changed aircraft twice and both times removed the trig units from the aircraft before sale, so i could fit them to my next aircraft (I now have a spare of each as the Nynja I have now already had trig units fitted when I bought it)
They just work, the head units could be improved in the area of usability perhaps but they are reliable and the built in intercom functions well.
Customer service has been first class, though I've had no faults I did send the radio back to trig for a firmware update and this was done free of charge with the units being returned in new original packaging as I had thrown the originals away years back.