I've never had a Thriantra (and not likely too either) but have had 3 tri-dutches and like all dutches they are absolutely the epitome of mischief. Great little characters, very inquisitive, generally pretty outgoing with people and not massively destructive. 2 of mine litter trained really well, 1 never got the hang of it and 1 was quite aggressive when I first got him but that was completely related to his previous home. He was an absolute doll by the time he left for RB.
The only thing I have to say is that of my three, one was with me for just 8 weeks, one for 6 weeks and the other for about a year and a half. Two had quite extensive medical problems and the other died very suddenly one afternoon. None of them were older than 2.5 years but they were all from rescue backgrounds (2 ex-breeding stock) and did have a history of neglect.