There's definitely a difference between "high" and "low" end; i stick to high, like aeb (or aeyow, or whatever the current iteration it is), though like sirloki mentioned you can tell they are all connected...
Its consistency of service, no guess work, clarity of menu, you get what you see in the photos, and
really truly gorgeous ladys; 90% of the time they adjust/adjust yourself to my last minute, now or never, schedule... I can schedule something on the fly, just like that...
I used them half a dozen times, never had a bad experience, some better than others of course.
And specifically I like that they offer 45min, most indys don't... that's my ideal length of time, in my head, thus I usually go for 1 hr with indys. 30 min is too much of a mission...
Lastly, with some indys, though friendliness and politeness is more than welcome, it can end up feeling like way too much courting/texting/dating...
The "low" is well, bargain hunting (no judgment, I can be plenty cheap, but for different things), the photos are a joke, its seems to be upselling anyway. I've seen enough chatter here, that i never used them.
Droning over.