Any VPN will give a bandwidth hit, lots of factors could contribute to the degree. The two real questions become (1) does the reduction in speed materially affect you for what you would want to do on that VPN connection, and (2) how does Google's VPN compare to others.
Found this post from one user comparing Google's VPN to SurfShark, where Google fared quite well; would be interesting to see how a wider range stack up, though again there could be a lot of other factors at play.
The Google VPN seems to work quite well as far as smoothness and very little bandwidth hit for my P7. When I trialed Nord VPN for a couple of weeks a while back I took a major bandwidth hit on all 3 devices I was using it with. I’m not to sure how much I really need a VPN honestly but since it runs so well and I can’t even tell any difference I’ll continue using it for now.