I wonder whether it depends on where you're traveling. I switched to Google Fi last year for the substantial savings (because I use virtually no data at home, and the basic phone service is about $20/month). I don't stream TV or movies when I travel, so I don't need high-speed data (and don't know whether Fi provides it, though it's supposed to be faster than T-Mobile). I just want basic internet access. I don't remember having significant issues in Norway and Sweden, but when I got to Finland things became frustrating. I was only in cities there: Turku, Tampere and Helsinki--none of which have a lot of narrow streets with high rises that could affect reception. All too often I had no connectivity. Then when I moved on to England (Sheffield, Manchester, Liverpool and London) and later to Italy (Ravenna, Padua and Venice) there were times when my travel mate using two different European SIMs had connectivity and I didn't.
The degree to which I struggled during the latter half of my trip was unexpected. In 2019 (when I traveled to Spain, France, Scotland, northern England and London) T-Mobile allowed me to connect a lot more consistently. One difference is that this year Google Maps is online rather than an app. A lot of my on-the-go usage involved Google Maps, and that change caused my data usage per month to more than double. Perhaps at least part of the fault lies with Google Maps rather than Fi itself.