Re vo2 sessions
TR workouts will change depending on how fill in the post workout survey.
You might get a few unproductive / easy for you vo2max workouts before it realises and bumps your level up to a more appropriate level. Equally for some people it might reduce the level.
Some Vo2max workouts in the library have the same stucture but a different precentage of FTP (there might be a version at 108% all the way up to 120% for 4x 5 minutes for example, which is a board range), it can take a session or two to workout which is the best fit at a given time for an individual.
If more experienced using resistance mode and just going best effort for the repeats is the best way in my opinion, using the precentage as a guide for the first but then go harder or easier depending on how you think you can complete the set.
Using the TR session and erg mode will probably get you 90% of the way there once it adjusts you level, but I personally dont think it that is near to optimal, however certainly good enough if you are not sure of your capabilities.
Out of interest what vo2max sessions seemed to easy?
PS there are lots of threads on vo2max intervals and TR, with good information in them. Search. Have a read and do what you feel is the best fit for you. 