Beside the amount of extra filtration that sumps can provide, the biggest factor for me (whether DIY or commercial), is ease of maintenance.
If there is enough clearance to get my arms in between the bottom of the tank, and upper frame of the sump, and pull in and out pumps or media is most important, or if to do those things I need to go into some yogic asana to accomplish it, is critical.
Before I'd buy, I'd get a cardboard box cut to exact dimensions of the one I'm considering, put it where I intend the sump to be, and put a couple rocks in it, to see if its easy move them around, or pull in and out.
Although chambers are aesthetically pleasing, I prefer functionality, and don't find chambers any more functional than tossing in bio-media, in mesh bags. They then are easy to remove, shake off the grunge, and toss back in.
Another factor for me, is whether or not the sump needs to be directly below the tank, off to the side, or even in another room, or on another floor.
Sumps do not need to be directly below a tank where clearance, and ease of maintanemce can be compromised.
One of my current sumps is (of course lower than the tank to accommodate gravity), but offset to make maintenance a breeze.

I have friends that put their sumps in the basements 1 floor down, or behind walls, for reasons like noise reduction, and to be in a place where the slop of maintenance isn't as critical, and where consistency of ambient temp is important (cool water fish, or ocean type temps are easier to regulate).
I mostly built my own from cheap old scratched up tanks, and prefer to spend extra money on more powerful pumps.
The one I have now is a commercial one, and came with the tank, so I use it, at least until the time I build a much larger one, with space enough to use other functional filtration types that emerge with advancing filter technology, or where one could add a planted section, refugium, protein skimmer or other methods.