The service will use Verizon's network (Verizon is the parent company of both Yahoo and Engadget, but that has no bearing on this report), and comes with the usual "unlimited" caveats. Times of high congestion will result in a slower connection, and tethering is limited to 5Mbits, with one tethered device permitted at time. Regular download speeds will range between 5-12 Mbps, with upload speeds of around 2-5 Mbps -- not ground-breaking stuff, but reasonable enough. It's probably not for you if you're a frequent traveler, as there's no international option, although the plan can be paused monthly if you're away for longer.
Predictably, you'll need a Yahoo account to run the plan, through which you can access the Yahoo Mobile app to manage your account and payments. It does come with a free Yahoo Mail pro subscription though, which includes 1,000GB of inbox storage. And, finally, you can opt to use the plan with your existing device, or get a new mobile. All the heavy hitters – the Pixel 4, the iPhone 11, and so on – are available.
It's a reasonable enough price plan with the backing of an established telecommunications carrier -- and unlimited data is unlimited data -- so for many it could be a convenient offering. However, inherent associations with the ageing Yahoo brand might be enough to put some off, not to mention the big question marks around its data security, having suffered a number of major breaches in recent times.