Has anyone added a small subwoofer to 2 channel and been thrilled with the result?


The subwoofer can of worms.
I’d like to add some bass to my otherwise fine 2 speaker setup and have limited space so perhaps a single 10in?
After a few weeks of research the only conclusion I can come up with is - everyone agrees they have to be setup properly. Every brand and technology has their own following and most recommend using 2 (which I don’t want due to space concerns). My room is 12 x 13 ft with box raised ceiling.
After much research, these are the subwoofers I’m trying to pick from, for various reasons:
Rythmik FM8  - lots of hifi fans
JL audio e110 - fantastic support
REL T/9i - sort of a gold standard
KEF R400b - interesting technology, makes me grin. 

I've never heard any of these.
System:
Hegel H160
SF Concerto speakers on stands.
Ben
casteeb
It's remarkable what a sub can do for mids and highs...I use a REL S/5 SHO, but have had great success in past with small REL in small room system...
A number of the Rythmik plate amps (all but the XLR models) provide both high-level connections (on speaker binding posts) AND line-level connections (on RCA jacks). You can try the sub both ways, and use the method you prefer.
I added an Omega DeepHemp 8 to augment my Super 3i Monitors. I was really unsure if this 8" driver (down-firing, sealed design) could be satisfying. It made a world of difference. Yes, I'm thrilled. I doubt you'd be disappointed with any of the ones you're looking at. 
casteeb, if you’re asking me, I’ve had a few speakers in there, most recently Canton Vento Reference DC9 speakers, which have a surprising amount of bass for small monitors and before that, Klipsch Heresy, which despite having a 12 inch woofer in a sealed box, don’t dig very low. The sub complements both sets of speakers nicely. I also use subwoofers in my main system with legacy audio focus 20/20 speakers which have a total of 6 twelve inch drivers.
Naive question: doesn't a sub mess with the image?

Say you've got a bass guitar mic'd mostly in the left channel but then part of that instruments frequency response plays over the sub which is in the middle of the two speakers. How can that possibly sound coherent image wise?