I have 2 of them and a vito
Tbh I hate driving them , they feel sluggish and noisy compared to the merc

Both are the 1.9 td 800 specials , they aren't common rail so don't think you can get tuning boxes for them . If I were you I would look for a 2.5 tdi as they seem much quieter and definately a lot quicker . Or you could allways consider a vito