Is there an advantage with using Straighterline rather than enrolling with a Univ?

[cookderosa]

If you already know that you will be attending a SL partner school, then you've really only got to consider cost. SL courses will not be covered under financial aid, so they would be out of pocket. You could also look into the cost of doing their full 10-course bulk package, and possibly save some money there. SL is not cost effective unless you are fast, but if you're fast, SL is a good deal. It pays to have your books already in hand when you start the clock.
Only other thing I can think of is if you decided for some reason that you couldn't stay at TESC or WGU and finish. In that case, a SL course likely wouldn't be accepted by a traditional college elsewhere, while the WGU courses certainly would.