Hi IanS1
I own both, cheap DIY MIG set and a combination of bit's that allows me to do TIG. I got my TIG gear about 30 years ago after watching a pipe welder repair a three branch manifold off my Mini Cooper(got to get me one of these i said)
The amount of times it has pulled me out of the *hit it was money well spent, it is so versatile, you can see exactly what your doing and you know you have got penetration, and with Argon you will be able to weld Stainless & possibly Ally if you flash a bit extra on a decent inverter set. don't get your gas from BOC as the yearly rental is extortionate. and i had mine in my shed for years just to have it on hand for when something hits the fan. I have used the MIG set and i think with practice i could become competent, but still prefer TIG.
Regards
Mike