You have to try them to see for yourself.
I've been using a set of the original Ashley Express Big Dot sights (no rear tritium capsule, just a white line) on my CS45 for many years.
Yes, they're fast and easy to see. A nice, big bright white plastic ring that stays cleaner & brighter than white paint (wipes off more easily, too).
I had to get used to covering the intended POI with the center of the front sight (instead of the top edge). Then, I had to get used to the "dot-the-I" alignment. It's easier than you might think to tip the front Big Dot one way or the other without really noticing it, though.
Yes, you can use it for adequate sighting out to very reasonable handgun distances (I shoot steel at 50+ yards), but it doesn't lend itself to "precision" shooting. At one distances I typically use for drills the Big Dot covers the entire "head" of the threat silhouette, while standard 3-dot sights can easily be used to sight a much smaller part of the threat target, making smaller grouped hits.
So, it depends upon your expectations and application.
I have the standard size XS front night sight dot on my pair of M&P 340's (factory sight setup for the M&P 340/360's). Instead of a wide rear notch and painted line, though, the rear of the snub top-straps have been machined to form a tight U-notch, into which the standard size front night sight fits.
This standard size XS dot sight setup is still very fast to acquire and use. I find I like the standard size dot better than the Big Dot I've been using on my CS45.
It's easily the fastest & mostly easily used sighting system I have on my more than half a dozen J-frames. It makes my J's shoot like full-size guns ... because I can SEE the sights, and they're still small enough to be used for greater precision than a much larger front sight.
I've seen a number of other instructors try the Big Dot sights over the years. Some liked them, most didn't.
They have their practical advantages & disadvantages. Try a gun equipped with them first, if possible. Not just at some gun store counter, but on the firing line of a range for some live-fire.
If I had it to do over again, I'd probably try the Trijicon HD sight setup before the XS Big Dot. Having found the S&W version of a U-notch to capture the XS front sight post so helpful, I prefer having more of a tight rear notch in which to position and align the front sight. The standard Big Dot doesn't do that.
I'll probably continue to use the BD's on my CS45 (although the front capsule is aging and starting to get dim), as I've become accustomed to them over the years ... and I'm too lazy to pull them and install one of the other 3 sight setups I have for the S&W 3rd gen .45's.
They work well enough for their intended role on that little .45 pistol, in my hands.
I think we have a wider range of choices available nowadays, though.
Just my thoughts.