To be honest I really don't recommend it. With RW, they will force you to join any nearby Wifi network - even if it requires you to accept its ToS and you haven't done this. So if you are waiting for Amtrak and the opposing train pulls up for 2 minutes, you are switched onto this network. Or if you are in a bus on the highway in traffic and you pass a Wifi hotspot, it will switch you onto it... Even if you turned off Wifi. It constantly turned on Wifi even when you explicitly tell it not to. Google Fi has not done this so far. And, if the public Wifi requires me to accept some ToS, Google Fi will keep me on 3G until I have accepted the ToS and am /actually/ on the internet via the public wifi. So, in the end, RW really pissed me off. Still, it is a cheaper service and as a college student it was all I needed. I stayed on one network 24/7 and had no complaints at the time.

Edit: One thing about being forced to switch to a network is that it is silent and you don't necessarily know if you are connected to the internet or not. So if you walk into a Starbucks that has public wifi and your wifi is turned off, your wifi will be turned on and you will have no internet connection until you accept Starbucks' ToS. This has left me very confused before missing messages, calls, etc.

I do a ~40 minute commute, and I'm not sure exactly what eatonphil is referring to. I can think of two possibilities, which are worth discussing on their own so it's not like I'm putting words in anybody's mouth.

One possibility is if you use a lot of data itself on the commute, like streaming audio. That would eventually be problematic (although 5GB is still a good bit of streaming audio). As I hate my audio being at the mercies of networks anyhow, let alone cellular networks, I play things off local storage anyhow, so I'm not sure about this in practice.

The other possibility is if your commute goes through more residential areas. I'm mostly commuting on a highway going through mostly rural areas and my phone has no WiFi to be confused by. But I have noticed my phone can be really annoying to try to use while walking to my car in a reasonably residential area, while it's busy trying to get one of the xfinity_wifi connections, and then failing, then I walk to the next xfinity_wifi connection... end result is that I end up turning off the Wifi radio if I really care. Would be more difficult if this happened in a car. (And some of this is Comcast's xfinity_wifi thing where all their modems now emit a secondary SSID for "other customer" access. It's neat when I'm visiting a friend's house that has it, but I'm yet to find it useful generically out and about.)

RW certainly mostly works. Perhaps it mostly works slightly less than a dedicated cellular provider, but it also costs a lot less. There's some quirks in the cell phones but I'm unconvinced all of them are RW-related. (The only one that probably is is that sometimes I dial, and after a couple of seconds it returns to the contacts screen like nothing happened, and then about a minute later dials the number. Not sure what's up with that exactly.)

Edit: My experience does not entirely match eatonphil's sibling post. When I turn off wifi, it stays off. It does get overexcited about connections being up when they really aren't, which I believe is more an Android thing (Android decides it has a wifi network, RW tries to use it), but of course it affects the service. RW is working on it now. Google probably has twice as many people engineering Project Fi as RW has employees, plus a lot of in-house Android experience they can directly tap for a custom Android distro.

I suspect were I not already a customer of RW, I'd go Project Fi, too. I'm definitely not annoyed enough with RW to incur the personal-time expense of switching, though.