Nest (Google) - OnHub (TP-Link)

I definatley would replace since it's hasn't received updates in over 2 years. If you are technically inclined OpenWRT is available for onHub. Performance was shockingly good with OpenWRT off GoogleWiFi puck except for SQM (for bufferfloat). It caps out around 190mb/s. If your Internet is below or around that it it'll be fine. Point being, you may not be able to enable SQM on onHub since it is even older and IIRC dual core instead of quad core like GWiFi, but at least it's been updated for vulnerabilities. As for buying, perhaps try OpenWRT on it if you are technically inclined. It isn't for everyone, but is rewarding.

To add to what others are saying, in addition to GWifi being quite locked down and having no way to access configuration via a browser (only via the Google Home app), the other problem is support. When Google no longer feels like supporting this version of the hardware, they will essentially brick it. They did exactly that to my old OnHub units. I cannot trust Google for networking hardware.

I replaced mine about a month before Google's final shutdown. Right after I bought my new hardware, I saw that OpenWRT was ported to OnHub! Too late for me, unfortunately.

I miss my TPLink OnHub, that thing was a beast until COVID and 2 people WFH and 2 kids schooling from home caused it to need a reset every other day and the range of the radio was getting shorter and shorter