As suggested above Peter H is a very knowledgable TB20 advocate his blog and forum have huge amounts of info.
I had an early TB20 (1984) for two years. I flew just over 200 hours in the TB and absolutely loved it! It had the most comfortable seating position it felt like being in a sports car bucket seat.
It cruised at the book speed of 145kts at 14GPh (low level). The W&B was good for taking four people some bags and a decent amount of fuel. It was capable of operating out of 500m Tarmac. The trailing link undercarriage was fantastic and made some more doubtful landings seem perfect! It was an all round well built aeroplane if you can forgive the slightly strange push switches. Nice to fly VFR and IFR. I only changed as I needed more seats.
Parts were never a problem for me, but I understand that they can be more expensive than say Piper.
Not sure if you know RateOne at Gloucester. They have one on the fleet might be worth trying to fly it as part of an IR renewal or training so you can get a feel for it without more commitment.