I like how easy it is, once you have an account set up everything becomes seamless in terms of scheduling tasks or tracking projects as they are coming along! It's not perfect but we've gotten used enough that most things work just fine without any issues at all (just keep testing!).
The free tier offers more than sufficient functionality so there isn't really anything wrong here either - if this doesn’t do what YOU need then perhaps try another service out instead? For us personally nothing about Groundkeeper has been too much trouble however sometimes when uploading files can be tricky depending upon file type/size etc which leads me onto my next point….