Monitor Audio FB210 or REL Strata ?

I think I'd go with the REL on that basis because the FB210 doesn't appear to give a significant frequency extension over your main speakers, and may give a nasty midbass hump because of the crossover being set too high.
If you're unable to demo the subs get the REL strata ... it's most likely to work for you. If you can demo them all then let your ears decide ... perhaps the FB210 will save some money.
I think buying the FB210 without demoing both it and the REL would be extremely risky. REL has a good reputation for a good reason.
Why not look for a nearly new REL strata for around $900 ? That's the best of both worlds.

Also, consider resale ... if this is a possibility then again this favors REL ... they usually resell within a day on Agon. The FB210 might be good, but I think it would be much harder to resell.

Thanks very much. I think I'm going with the REL. I need to buy a black finish, so can't find any as new REL, but I've dealer for REL in my area, will get a new one. Also as you have mentioned, resale value.

If you haven't heard a quality sub in your stereo I think you're in for a treat. My strata transformed my CD collection. Some of the live CDs and large orchestral pieces are so transformed I'd find it hard to go back to no sub. Have fun !

I owned a REL Strata II which I used to good effect with a pair of B&W Nautilus 805s. Then I upgraded to Audio Physic Virgo II speakers. I then found I got better results on music by disconnecting the sub, and I ended up selling it. The Strata II certainly was able to add more to the bottom end, but the quality was not on a par with what the Virgo IIs were delivering - either that, or the sub was just not integrating well (and I played with the settings a lot). I found that the sub added more, but, as the saying goes, 'sometimes more is less'. Just my two cents. Good luck.