You can't buy heritage - and I'm not sure that Sinn has all that much to boast about anyway. Some MKII designs I have seen - like the Kingston - look really terrific. Some are kind of 'meh'. With any boutique brand, there's an open question as to whether they will still be around next year or the year after. But given the use of standard ETA movements, I wouldn't worry too much about future servicing.
I've owned a couple of Sinns over the years - nice enough watches but I never fell in love with them. And they are getting kind of pricey for what they offer, in my estimation. Most of the pieces in the 3-4k - plus range do not represent good value, IMO. The more basic models are a better bet. What watches were you considering?
You might want to look at Damasko as well.