We are currently looking at another stand alone system that costs about 1/2 what the TEC3 does. Like stated above, the main benefits of a system like this is that there is less emphasis on emissions and more emphasis on WOT tuneability. The SCT system is an excellent adaptation of the stock setup and more than enough for an SC making at least 450rwhp. For applications using lots of nitrous, turbo's, or boost/rpms in excess of what an M90 can do, then a stand alone system *may* start to look a little more attractive. Of course a stand alone system is only as good as the tuner so while it can be a benefit, it can also be disasterous for your engine if you don't know exactly what you are doing.
People have carbed the M90 before, but there is no reason to do that. If you understand enough about tuning to be able to tune a carb for use in a blown application, then tuning your EFI is a walk in the park.