I've bought 2 $20 Diamond washes from Octopus and here's my verdict:
+Relatively quick...
+Friendly staff inside
-They will annoy you with a sales pitch
-They only spent 5 minutes on my car and it shows. Spots, cheap wax, and the interior was barely touched, save for a "fragrance" boasting the subtlety of a cherry shoved into my brain.
I'm buying my own cleaning materials, befriending someone with a hose and cleaning my car myself from now on. I paid $8 for a wash in Atlanta at Cactus Car Wash with better results.