As is fairly obvious now, there will be a trade-off as there is in most things.
Basal-IQ (currently available) will allow lower BG numbers. So if one is already quite expert at managing high BG and manually knocking down the BG quickly, the Basal-IQ is great at preventing lows and for overnight via Basal suspends. Right now with Basal-IQ, we are almost always waking up straight line at 80 BG. This is pretty amazing.
The Control-IQ (launch forecast Summer 2019) will add a great deal of automation including basal suspend as well as both basal and bolus increases. Control-IQ will work on both high BG and low BG. This is going to be great for the vast majority of people interested in Tandem pumps. However the trade off (as obvious from the review that @Anthony posted) is the target BG will be higher in Control-IQ then Basal-IQ.
Although not mentioned in the review, I believe the waking and non-exercise target BG will be 112 for Control-IQ.
Tandem has already publicly stated that this first release of Control-IQ is not the end of the road. They will continue to work on it, enhance it and make it better.