There is nothing in REL subwoofers that make them inherently easier to integrate. OTOH, SVS subwoofers provide some tool that could help the integration process.
REL success in the market is due to good marketing, aided by the falsities of the High End Audio press. They are thoroughly surpassed in term of measurable performance by the usual suspects (SVS, HSU, Monoprice, Rythmik, etc) and many others. They are overpriced. Don't fall for the marketing BS that says that using the speaker signal makes them more musical or easier to integrate : it is utter BS. Provable. The reference when it comes to subwoofers
Sweetchaos Subwoofer Comparison .
I hasten to add that subwoofer integration to main is
not impossible, it remains difficult. It requires lot of measurements and, reiterations. Another added complexity to the process of integration, is that the better results are obtained with multiple (as in more than one) subwoofers which increase, manyfold, the difficulty of integration. To make things even more complicated, the DRC/DSP/EQ in many AVR do not do the greatest job when it comes to integrating subwoofer and mains. Audyssey, for example, requires manual adjustment (At least for me and from reading fora, most people), DIRAC with all the good will and great buzz does not either; unless you count the rarely if ever present DLBC, which is an add-on, not part of the usual DIRAC. Many audiophiles use an external DSP/EQ component, one of the often used is the miniDSP 2x4 HD. And, yes, it takes time to make this work, and patience, and determination, and research... Good integration of mains and subwoofer (singular or plural) , mandates the use of a measurement microphone such as the UMik-1 and software such as REW and/or MSO. The last two would never win a contest for ease of use, let alone to master. MSO in particular is powerful for multiple subwoofers integration, but it takes some (a long?) time to get the hang of it... Let's go ahead and call it "difficult"
. And you still need to have a good grasp and understanding of REW to achieve good results with MSO ... So .. No! Subwoofer integration is not easy. I would go as far as declaring that, optimal results are rarely achieved by most.
It is also safe to say that it is impossible to achieve great subwoofer integration with mains without DSP and EQ.
The above holds for any subwoofer.. REL included.
Peace.