Mix and match subs?


I have a Paradigm x10 sub and am planning on adding a second sub. 
Would integration be difficult if I a) got a 10 inch sub from another brand (thinking SF Gravis III to pair with my SF speakers); or b) the x12 from Paradigm (for getting even deeper).

Or c) should I just keep all the same and get another x10?
w123ale
Seems like there are differing opinions on to pair or mix and match. 

Has anyone mixed subs with two driver sizes and had a bad result?
The majority of posters say mixing subs is not an issue.  I'm guessing that those are people (like me) that have actually done it.  I have two Rythmik F25 subs (2 X 15" drivers) and two SVS SB13 Ultra subs (13.5" drivers) and the result is very good!
I haven’t had any problems with my B&W and SVS subs. I don’t think it makes a difference in terms of subs. 
You can mix and match subs…but, you need to measure the in room frequency response at the listening position to see how the varied bass settings effect the sound. Ideally, something that gives you a visual to see in real time your settings as they change to help level out the curve. I use an old school Velodyne SMS-1 subwoofer Equalizer with a microphone and test tons to see in real time how all of the sub settings blend at the listening spot. I shared a link with my rudimentary measuring setup with a before measured response curve and after…note how much flatter it is after tweaking the settings. Not all flat curves are ideal, especially if you desire more bass and care a little less about microdetails. It is a personal choice, but it is important to eliminate as much drone, boom, and resonating bass which helps increase listening pleasure. 

https://www.amazon.com/photos/shared/I_6Rau1zQcOKOTfMsFSy1A.-ZXzEvmp6JEbBSJWepTMIw