Project Fi won’t be challenging the major carriers anytime soon, but it does offer a compelling package for those that stay in range of Wi-Fi most of the time, as the flat $10/GB data rate plus the base $20 is a very inexpensive starting point.

For those that have already signed up for Fi, another enticing option has been added today with the ability to tack on a data-only device at no additional charge. So while you need to be an existing Google Fi subscriber and paying the $20 Fi Basics fee, there is no charge for adding a data-only device. You order a free SIM card from the Account page within your Fi account by selecting Your Plan and then Add Data-Only SIM. Data is shared between your devices, so if you use 500MB on your smartphone and 1.5GB on your tablet that will be a $20 data bill (plus the $20 Basics) for you at the end of the month.

Unlike the smartphones, which will switch between T-Mobile and Sprint for optimal coverage, the data-only devices are locked to T-Mobile. Data-only devices supported at launch are the 2013 Nexus 7, Nexus 9, Samsung Galaxy Tab S, iPad Air 2 and iPad mini 4.

I’m not sure if this is going to be the tipping point for anyone to jump on the Fi train, but it’s good to see Google adding features to the fledgling service.

If you are a Google Fi subscriber, we would love to hear what your experience has been like with the service.