This is one of those questions that must be answered by each individual, for whatever reasons seem more important to
them.
Now, unless the new bill in committee (CA state) to repeal the state's Roster of handguns that can be sold somehow passes and is signed, this is a moot point for me. Since I no longer qualify for the peace officer exemption for buying guns not on the state's roster, I won't be buying one.
However, having been an unwitting Beta-tester for a new model pistol in the past, I've long since decided that I'd just as soon give any new pistol design at good year's successful production time before looking at it for myself.
Notwithstanding the Beat-tester concern, though, after many years of continually buying new pistols, justifying them as being used for off-duty and firearms training equipment, I've lost my zeal for buying new guns just because they appear to have some minor "advantage" or improved feature. I prefer them to have a significant advantage over what I already own ...
or, at least be a "duplicate" of something I already own and have found to have a lot of merit for its intended role.
If the Shield 9's 7/8+1 mags and topped-up capacity is something someone considers to be a "significant disadvantage" compared to a 10+1 option? Hey, it's their money and their choice on how to spend it.
Whenever I've been asked the seemingly inevitable question about "capacity" by some of the people I've helped train over the years I've served as a LE firearms instructor, I usually respond with a question of how satisfied that person might be with their just demonstrated "results" during some training drill or qual scenario. In other words, were they satisfied they were as competent and skilled as they wished to be in getting those first 1-3 hits on a threat, or 2-6 hits spread among 2-3 threats (for the really "busy" scenarios that might have more than 2 recognizable threat targets).
If they acknowledge they aren't as comfortable with their skills-set and abilities as they wished, I ask them if they're hoping more ammo capacity will somehow "make up" for their unsatisfactory skill levels? (A "loaded" question, but not an impractical or irrelevant one, I think.)
Just because they may have the potential ability to shoot 2-3 more rounds before having to again load isn't exactly an "ideal substitute" to spending more time working on getting more skilled at getting those first 1-5 hits.
Now, there's nothing "wrong" with wanting "more" of something. I remember when Colt used to use the sales pitch that their Dick Special .38 snub had 20% more ammunition than the S&W Chiefs Special, because it held 6 rounds instead of 5. Some early 1911 aficionados seemed to flock to the idea of going from 7rd to 8rd mags (which wasn't always what they wanted after having feeding issues with some early 8rd designs).
One of the first things some eager Glock G43 buyers wanted was ... more rounds in their magazines. They wanted +1 & +2 extensions. They wanted a small, slim single stack gun to essentially have the mag capacity of a double stack. You just can't please some folks.
Now, me? Well, let's just say that if I were to return to active duty tomorrow, and could once again enjoy the peace officer exemption for buying off-roster guns ... I'd still wait another several months until SIG has put between 250,000-500,000 P365's out in the hands of shooters, and those shooters have had a chance to wring them out for a little while. Nowadays I prefer for others to be my eager Beat-testers,
Gotta suit yourself, though, It's your money.
And if you're planning to carry it as an actual dedicated defensive carry weapon, it's your life.