We got homelink set up recently and the convenience factor is awesome. The garage door open/close automatically at a set distance, the mirrors fold/unfold automatically, and I can control all my garage doors through the tesla interface. I can come and go without "breaking stride" and ensure my door is always closed when I'm out. While some may not feel it is worth $300... it's a whole lot better than alternative of having a bulky manual opener or dealing with your phone. $300 over the course of multiple years of ownership and peace of mind that I haven't left my door open is worth it to me.
In terms of install etc... once the box arrived, I set up an appointment with mobile services. Setting up mobile service appointment was painless and only took seconds. The tech confirmed I had the homelink in hand (via app) and scheduled the install for free. The install took a matter of minutes. The only real hiccup I experienced was, unfortunately, I have an older garage opener (my problem, not tesla) and it tends to be very finicky, even with its own branded remotes - though we did eventually get it to link up. The tech took a reasonable amount of time to try and set it up but after about a half hour of trying, he said sorry, there wasn't much else he could do and that I'd have to figure it out for myself from there. While annoying, I get it, the issue was with my garage door opener, not with the homelink or the car. In the youtube videos we watched, people were able to stand in front of the car, hit the button, and it immediately linked up. For mine, I had to hold the remote button for what seemed like an extraordinarily long time (probably a good 30-60 seconds) before it recognized. But once it did, we were good to go!