The Great Waaagh! detachment is 'out of date' now that the updated Waaagh! Ghazghkull has superceded the old book, the supplement now solely consists of formations and the new decurion-style detachment. If your opponents don't mind you using the old version then you can have as many supplement relics as you like though. However, because of the Boss is Watchin rule and the small size of your units you only have a 1/6 chance of passing a mob rule test - pretty terrible detachment in my opinion. It does give you access to the nice relics though, and if you're just playing for fun that might be worth it for you.
There's lots of upgrades here that probably won't be very useful (grot riggers on Trukk, attack squig, supa-cybork, extra armour etc) but Bad Moons are more teef than sense anyway

if you're going for fluff then who cares what we think, just make sure those lootas aren't stealing from your own gitz!