I have it and I love it. Got it for the reason you're quoting- back issues after bathing in the tub. The price did hold me back at first, but I got a really good deal at a dog show (on the last day of a four day trial).
We also go to a regional dog park here where there is a bathing facility with elevated baths. I go there frequently enough that now I pretty much schedule her baths around those trips. Since the park has access to salt water, we probably use the bath facility more frequently.
But now and then I still put the Booster Bath to use. I'm glad I have it.
And there are alternatives out there.