I have had a broken nail for years on one finger, and it just keeps breaking on a regular basis. I found this on Ebay, and thought it had to be worth giving a go.
It is basically a tube of glue and just a tiny bit on the broken part of the nail sticks it to give time to repair. It is a bit messy as just a slight squeeze puts quite a lot on the nail. If you are a bit heavy handed it will go all over the nail.
It does stay on the nail for quite a long time before it wears off and does the job. The broken nail does stay together, but as for a full repair? I would say it would take quite a few applications over a long time.