I went ahead and installed the combo slide with Romeo 1 Pro red dot sight on my Sig P229, 9mm. Runs great, dot is nice and easy to pick up 6moa. The slide and the sight are top quality. I've taken it to the range twice and put 260 rounds through my P229 with the red dot set-up. I will say that I shoot a little more accurately with it over the 3 dot sights but not really by that much. I suppose the red dot would be a superior sight to use in low light situations too. Don't know if I really want to keep it or let it go. Do these sights grow on you over time? Right now I don't feel like I got my money's worth out of the purchase. You might see this slide & red dot in the classifieds.
Red dot sights, either RMR or those projecting onto the target, take some getting used to. Especially the RMR types. With the RMR, it becomes critical to present from draw already lined up on target, which is a useful habit to develop.
With either type, it allows you to focus on the target, not the front sight blade 4 or 6 inches forward of your knuckles. That is a huge advantage! You will especially appreciate it as your eyes get older. If you aren't already there, that day will come. You won't realize it until after it happens.