Definitely don't commit to a free service without planning for a transition when that service changes.
Fortunately Tailscale is built on Wireguard. So it's an easy way to get started with Mesh Networking, and then you could transition to Wireguard if needed.
Hamachi did the same thing 20 years ago, and is still around (I think) with a free tier that lets you have 250 clients. It just doesn't have mobile apps, which is a show stopper for me.
Tailscale also has the "Funnel" feature, which can route traffic into your Tailscale network without using a Tailscale client.
I'm currently on a free tier of TS, and will have no problem paying for the service once I go production. It's not expensive for what I'm getting ($50/year IIRC, because I'm one user). Could be a little pricey if you pay per workstation (so using the subnet router option would save subscription cost).
I could just switch to self-hosting Wireguard, it's the protocol Tailscale is using.