The Rug Renovator kits from each G series model can be used on ALL G series models, so you can use a Sentria one on a G3 and a G3 one on a Sentria, may not look right but it will work fine...
The hose on the G3 works on the G4, but not the G5 or newer (I'm not sure what newer hoses are compatible with each other). But yes the shampooer works on all of them.
The floor polisher is one of the few attachment I think I'd use so I thought I'd take a chance and pick up the Ultimate G one to see it it worked on my G5. Glad to hear that it does!
"(I'm not sure what newer hoses are compatible with
The G3 to Sentria hoses are all the same, the only difference is the motor end of the hoses for the G3 & 4 have a rubber seal in them to seal on the fancase, but the G5-on models have a Unigasket on the fancase so have no need for the seal on the hose. You can actually use a G3 or 4 hose on G5-on models, you just have to pull out that rubber seal first and you can use the later hoses on the G3&4 if you replace the floor nozzle seal on the fancase with a Unigasket...