yea there both TDi realy, just the common name for the earlier one is "The TD"
The Tdi will start quite happily under almost all circumstances without preheating with the glows - so they're not absolutely required. Personally I always use mine as it will start quicker (any diesel engine will with preheating) and more damage is done to any engine during the starting and warm up than at any other time.
Cheers,