I have many; think women shoes; the best of both Worlds is a Dillon 550 it can be used as a single or progressive. My experience and opinion only
I think there are other progressives that can be used as single stage. I have the Hornady LNL Pregressive and use it as a single stage. Sometimes I will use it in combinations. For example I use my FL die, Neck Die and Pin Gauge die at the same time for sizing. I ensure that the two dies that are creating the most force are opposite of each other and as close as possible to the posts to limit any flex.This is also beneficial as I also use a delay process where I allow at least a 10 second delay before retracting the case from the die.
When it comes to seating, I only use one die and it is positioned right next to the post.
For less critical rounds, like my 45ACP which is my non competitive, play gun, I like the progressive action. I tumble my rounds, then all in one, decap, prime size, powder drop, drop bullet, seat bullet and done. Makes reloading a lot of ammo very easy and quick.
All this being said, I have contemplated purchasing a single stage to see if it would be any more precise than my progressive. I get less than 0.001" runout on concentricity, the seating depth, provided I separate my Bergers first is <0.001". I don't know if I would be able to improve much on this. But I can see the advantage of a single for some operations.
Bottom line, I am glad that I purchased the progressive first. I have learned to use it to do much more and not sacrifice convenience. But now I can look at other options to add to it when time, space and money allow.