There's some lock in in terms of framework specific code but no lock in of your data,it's just a mongo dB. The reliance on mongo means it's always a bit tricky to make join-like calculations, but otherwise I'd really recommend the meteor stack. For hosting as a side project I'd recommend a shared digital Ocean droplet, you'll get much better performance than heroku. Use "meteor up" to deploy. It will be 5usd per month but you can host many small apps on one droplet