The TB20 is a groundhog, and I speak as an owner of several.
For an aircraft of its horsepower, the take-off roll is not exactly sparkling, an effect that is more marked when heavy.
St Marys is hardly a tough test of a light single. Let's see IO540 fly it onto (and away from!) Lundy, and then we can talk.
The two selling points of the TB20 are its range (326L usable at 50L/h and around 150 knots) and its useful load.
In the non-GT form, it has limited headroom for tall blokes with headsets on, and the avionics can be a pain to work on.
Other than that, a nice aircraft
2D