I can't comment about the differences between this and the M6, as I've never had an M6 or M6TTL. I had an M2 for a year or so, and it was my favourite camera. Even wrote to a forum (this one?) about the possiblity of putting a meter on it.
Then got the M7, and it is the only Leica I have owned which I really didn't like. It felt too automated, too much like any other semi-automatic. I didn't have confidence in it. I have a IIIf which is better than the M7 was.
So after getting remarkably little for it (below 50% after less than a year, with lots of passport still to go) I plunged and got an MP. Fantastic, and my credit card has now bought another one. It feels more like the M2, and is a delight to use. Never quite trusted the M7 and literally would not have one given, except to sell.
With the MP, Leica were so supportive. Bought one from Ffordes (great company I regularly use), but there was a mistake on the website, where they offered a free motor wind. The offer had expired two or three weeks previously. Rang Leica, and they said, don't worry, you'll get it. It arrived next day. Then said to the nice lady, I bought my first MP a week before the offer opened. (You can tell how keen I was, after selling the M7.) She asked me to write in and explain. A Leicavit arrived a day or do later. This was a mistake - hated the Leicavit (slightly rheumatic hands made it awkward). Still, I thought, I'll keep it, as they have been very good. The nice lady rang a day later to ask if I was happy. Explained the position. Next morning a motor wind arrived, and they collected the Leicavit.
With service like that, who should worry?