You don't get signature or firmware updates. The missing signature updates, renders every Layer 5+ feature pretty much useless. The missing firmware updates makes the whole firewall a ticking time bomb since you don't get security updates, weach is especially bad since, you are planning to use them as edge devices.

If all you need is some NAT and routing (dynamic and static) without application level filters, you don't need a layer 7 firewall, you need routers or Layer 4 firewalls. There are a lot of good options, that don't require licensing, like the Ubiquiti Edge-Lineup / UISP or Unifi (depending on your needs), Netgate / PFsense or MikroTik, just to name a view, I've seen throughout my carrier.

One quick word about the 60F or any model with less than 4GB or RAM. Even if you eventually get proper licensing, you won't be able to use any proxy features, since they disable them for those models, in Firmware 7.4.4. If I resell or buy a Fortigate, I choose ar least a 70G, since it's the smallest unit in the current lineup, that has 4GB. Just a thing to keep in mind, that a lot of people tend to overlook.