Using Tefzel wire without concentric twisting

If I want the benefits of higher temperature resistance and a proper bulkhead connector, but I also want to save time on the build and avoid concentric twisting, are there any reasons I shouldn't use Tefzel wire and an autosport bulkhead connector? If my setup doesn't have particularly sharp bends, and the vehicle is primarily a street car with occasional track use, the time cost / benefit of twisting seems questionable to me.

No reason -- I built hundreds of harnesses over the last 25 years using Tefzel and only once bothered to do a proper concentric twist (repair of a pro-built harness that was damaged in a fire). If possible I would still twist (as opposed to running straight/parallel) each leg to allow as much flexibility as possible.

Super late to this topic but I thought I'd add my two cents.

I've done it both ways, twisted or just straight run. If you are going to do a straight run I'd be careful(or avoid) sheathing it in DR25 which most people default to with tefzel from what I've seen; you didn't mention what covering you were using so this isn't pointed at you specifically but anyone that might come across this. The first time I did it for a customer for his club level motorsport car once it was done it was incredibly stiff/rigid. After that happened I played around a bit and came to the work around where you have to pre-form the main trunk to the shape of the engine/routing before shrinking. In essence put whatever bends required to force the DR25 to shrink into that shape(like making a curly cord) but even then with the individual branches/break outs twisting is required to get decent flexibility in my opinion. But to that fact twisting a couple/few wires together is pretty easy unlike doing a main trunk of a harness.

Not everything needs to be twisted and the harness with straight runs should work perfectly for what you need it to do.