I think the audiophile that wants a subwoofer that "hits hard" and in my experience wants to know the subwoofer is there will love JL Audio subwoofers. REL Reference subwoofers are for the audiophile that wants a subwoofer that disappears to the point that you wonder if the subwoofer is on, but when you turn it off it's clear how much it impacts the soundstage, detail, and bass articulation.
I want both. A sub that is clearly working (really a must with my monitor/subwoofer system) and "hits hard" when it should, and one that at the same time also disappears into the entire sonic picture and integrates seamlessly, without timing/timbral issues that make it stand apart. I have all these things with my dual JL Audio F112 v2s. I don't see that as a REL vs JL Audio issue.
And yes, the extra adjustment flexibility of the JL Audio over a REL is a must for me. The extreme low-frequency cut-off function is a "life saver" in my medium-sized room, and I could never live without the phase adjustment on a continuous scale that the JL Audios provide (rather than a 0 or 180 degrees option). My subs are now at 55 degrees phase after careful adjustment by listening to many different kinds of music and recordings.
I used to have REL, but I am very happy with the switch.