How important for surrounds to match fronts?

I've done it both ways and gotten good results both ways.

My listening room does double duty as a home recording studio. Since I use a pre-pro in my 2 channel rig, I'm able to quickly go surround if needed for an audio-video session. I have a small Marantz projector and use 3 of the 4 powered M-Audio monitors that are usually dedicated to the recording studio or connected to a remote Sonos zone as surrounds and a center. These M-Audio monitors are both less than optimal for surround duty (dispersion) and very different from my main speakers - usually Ohm 100s, sometimes MMGs, occasionally Verity P/Es. In all cases, the results are satisfying to me.

YMMV

It may or may not make a difference. I had Focals as surrounds paired with my Revel fronts. There was a difference. One wasn't necessarily "better" than the other but it was different. When I replaced the Focals with Revel S30 surrounds, I only then appreciated what the full voice matching did for the surround experience. It was truly seamless.

I think that matching all speakers and timber matching is critical to the home theatre experience. I do think that when creating a home theatre like the movie experience the only way is with horn drivers-like the theaters have. The heart pounding dynamics are only created with a full horn loaded speaker. Plus subwoofers to add those last octaves. Take a look at Casta Acoustics and see what I am speaking of. Custom horns are simply amazing. You will not need another speaker.........

If you are focused on non matched speakers during a movie then turn it off.....its a bad movie. Speakers within reason will be fine.

I personally care nothing for multi music surround, but rather only movie surround. That said, by far, I find that effective diffuse dipolar or similar type surrounds - which are EQd out from the main processor, to match the timber n response of the mains - which envelope the listening area, are of more importance than matching or identical speakers all around. But to each his own. (Surrounds at most movie theaters not same as fronts either!?)
The main fronts n center are BY FAR the most important for anchoring the front soundstage, n carying the content, IMO. The surrounds are mostly for carrying secondary ambiance cues,and should be placed so as to not be localizeable, create a large diffuse side and rear soundstage, and for "fill" (as a priority order, that is -minimumally speaking). Thankfully, it's also most impractical to place larger, even full range, direct firing traditional loud speakers up on rear walls n ceilings, anyway.. Not to mention decor eyesore!
Yes, mostly match main fronts, n work on system set up n integration, proper crossover response n placement, and EQing, I say. let the diehard audiophile music only lovers worry about 5 or more matching speaks! The wife or girlfriend will never love it anyway, otherwise.