Indeed it might be slightly less flexible and it does mean if you have a problem with the TSOE then you probably wont be able to run the train unless you have a spare TSOE but that's no different to a multiple unit, I guess it makes it similar to a HST in terms of flexibility in that you can take out and add coaches in the formation but you still need the 2 end power cars or in this case a DVT and a TSOE.You can take out intermediate vehicles though as required