If it's a relatively new sub, you may not get much actual hands on experience. I would get the SVS before I'd get a REL.
With the high efficiency of your JBL speakers, you want a sub with some power and most will recommend a sealed design for music. I have a combination of two SVS SB 13 Ultra subs and two Rythmik F25 subs and have used them with high efficiency speakers like Klipsch Chorus. SVS sealed subs are fine for music and their newer ones offer nice setup options.
If it was me, I would consider getting 2 (or more) smaller subs to help combat standing waves. I would look at Rythmik in addition to SVS.
Your JBLs go pretty deep on their own and you just want to fill in that bottom region that they don't quite reach.
If you are space / budget limited, then one big sealed sub is not a bad way to go, but you may have some peaks and nulls in your room. Adding more subs will help with that and also give a more realistic sense of "being there" listening to the music being played live.
I'm hoping the post about the Tekton "Cinema" sub was either a joke or a troll post. A 300 watt ported sub that appears to be designed for home theater is not what you want.