I got my Carista OBD reader yesterday, there was a deal on Amazon and it came down to £15. I’ve also got 1 month free access, then £49 a year thereafter.
Seems good so far, plenty of scope for changing things if you want to.
Word of warning though, I made a rookie mistake… after about 45 minutes of messing about with it, I drained my battery

Turns out the battery wasn’t holding charge and was 11 years old, new battery now fitted and all is well in the world again.