Motorola’s 5G Moto Mod was technically the first commercially available 5G device — a backpack that enabled the 2018 Moto Z3 phone to evolve from 4G network support to 5G millimeter wave connections over Verizon’s mobile 5G network. Now Motorola is adding 5G Moto Mod support to an older Motorola phone, 2017’s Moto Z2 Force, expanding the base of users who can enjoy 5G speeds. But there are caveats.

The good news is that the 5G Moto Mod remains the world’s least expensive way for users to experience some form of 5G. Back in March, the accessory was offered to early Moto Z3 customers for only $50 with the use of an early Verizon 5G plan, a super cheap way to bring the $480 Z3 onto the carrier’s 5G network in the two cities then covered. The device is now available at its standard retail price of $350.

Since the Z2 Force phone was being sold for as little as $100 last year — it’s off the market now — that brings the total price of a “5G device” up to only $450, less than half the cost of a new phone with 5G built in. Motorola promises that Z2 Force users in Verizon’s first 11 5G cities — and over 30 cities by year’s end — “will be able to download high-definition videos and games in seconds” but stops short of providing specific download speed guarantees. Also, recent unspecified software improvements to the 5G Moto Mod will apparently enable “faster speeds across the entire Moto Z family.”

Adding 5G Moto Mod support required Motorola to update the Moto Z2 Force to Android 9.0 Pie, which it had promised to do across multiple carriers’ Z2 Force models. While the company released a Pie update for the Verizon Z2 Force earlier this year, it stiffed non-Verizon Z2 Force customers, nonchalantly noting that it had decided not to deliver the Pie updates they had been promised.

One of the biggest potential concerns with using the Z2 Force and 5G Moto Mod together is battery life. Motorola says it has enabled bidirectional battery sharing between compatible phones and the 5G Moto Mod, with a back-and-forth refueling process that takes place once the phone hits 15% or the Mod hits 13%. Notably, the Z2 Force shipped with a relatively small 2,730mAh battery, and the 5G Moto Mod adds only 2,000mAh of its own power, so heavy users may well find the combination less than ideal for extended 5G data sessions.

Motorola is using the announcement of Z2 Force support as an opportunity to subtly encourage buyers to replace the phone with a newer, faster Moto Z4, which also supports the 5G Moto Mod. The $500 phone is temporarily being offered for $240, paid over 24 months, with the 5G Moto Mod remaining at its $350 price. If you’re an early adopter interested in trying out 5G, that’s only $590 for the hardware, though you’ll need one of Verizon’s confusing and expensive “unlimited” phone plans and access to one of its currently scattered 5G towers.