I've got both a Mk3 Nikko, bought new 3 years ago and a T50 thats about 3-4 months old. I used the T50 on an s400 in GP1 this year - scored 30, used my Nikko on my ev2 at Gp3 and scored... 30.
New one £400 with sunshade, caps & guarantee.
T50 is 10% lighter than the mk3 which is 10% lighter than a mk2, which is lighter than a mk1
Turrets are a better shape if you don't want to spend extra on a big top turret
Available second hand (but a good one even if it's 10 years old will cost almost as much as a T50)
Can get mildot or Nato ret which is finer than the T50
Head position less critical ( but I think thats a disadvantage in the field)
I wouldn't hesitate to use the t50, Jon Harris uses one regularly and won a couple of MFTA WL's last year so they ain't bad.
EV2 mk2 with 2009 big Nikko
HW97K with 6-24 Nikko Nighteater