Remember it's a long time since, I played with it.
Things might be better now.
1. Yes it was reliable. But when connected to a master, there were a (to) log delay between push and sound.
2. I didn't try HomeSeer. But I am quite sure, It can be associated. If Homeseer is able to send it a "basic on", I don't know.
4. I can't remember. I think it was ok.
5. As wireless doorbell yes. For HA it wasn't good enough 1½ years ago.
I hope it was a little help.
Unfortunately I only played with a demo, I never used it i daily life.