Rear sight adapters suck. If you aren’t sure whether you will like a red dot and want to try it out, then a rear sight adapter is a reasonable solution for a range gun. I wouldn’t trust one for defensive purposes. If you know that you are going to change over to using dots, then direct mill.
Like anything, dots have advantages and disadvantages. They are expensive. The must be installed correctly. The battery must be changed once per year. You need to keep the glass clean. Every time you pick up the gun, you should check that the red dot is still working. You MUST train with them so that you see the dot on the draw. They add bulk to your gun.
But they also have advantages. Beyond 10 yards they are much faster and more accurate. In low light they are like cheating. You can shoot with target focus while also seeing the dot. For old people like me who need reading glasses and have a hard time focusing on front sights, red dots are awesome.
The RMR is a very good red dot. What sucks about it is that you have to remove it from the slide to replace the battery. After that you will need to go to the range to confirm zero. You’ll need the appropriate torx bits, a small torque wrench or torque limiter, a degreaser, a paint marker to create witness marks, and thread locker to reinstall the RMR — it’s not hard but you need to do it right or the screws will back out.
I’m not a big fan of the RMRcc because it has a proprietary foot print. Most of the compact red dots use the Shield RMS footprint.
I’ve had good luck with Holosun red dots, though I don’t have as many rounds through them as my RMR. You can change the battery in a Holosun without removing from the slide.