There is actually a difference (not a HUGE one but still, a difference). They are ROUGHLY the same size but definitively have a difference especially with the brackets being used.
I had Rigid's in my rear bumper. The Honeybadger bumper was built for the Rigids. I swapped them out for Squadron Pros. The Pros sit a bit back in the bumper then the Rigids due to the bracket. Lights are very close in size but it's the brackets that are different.
Here is a Rigid D-Series next to a Squadron Pro. The Squadron has the flush mount bracket on it as I was comparing some outputs (Their Wide beam vs the Baja work/scene, which I prefer for reverse to illuminate a lot more up close then a spotty style pattern)
Squadron Pros are 3.069" in width/height (the light itself). With the brackets installed it brings it to 3.313" height wise and a depth of 2.765" total
The D Series (surface mount) is 3.2" in width and 3.2" in depth. If yo use the heavy duty mount it brings it to 3.8" tall
So very close in size BUT slightly different... the biggest difference is the way the brackets make it sit IF you have cut-outs for the light. It wasn't enough that it bothered me... my lights just sit a tiny bit recessed now in my bumper compared to almost flush with the Rigid.
Let me know if you need pricing of course on either. I have every type of Squadron in stock with every type of lens.