Yep, I use the locking nut on all my guitars that have them. Most of my guitars have floyd bridges - I'm not a huge divebomber but now and again I might go for one.... :)

Once I stretch the strings in and get tuning stable I can lock the nut down and the guitar will stay in tune for as long as the strings last... maybe a minor touch on a fine tuners now and again but I have no problems. The points the guy makes against using them could easily be resolved by learning how the assembly works, and arguably by buying a better quality guitar with a better quality bridge.

To take his points in turn:

1 - No tuner post is going to keep your strings secure if you're a trem abuser.... and if you're not, why have you gone for a guitar with a double locking trem?

2 - Debateable, but I've never had a string break at the nut. They always break either at the bridge due to the extreme break angle or right under my fingers from my enthusiasm... I doubt this has much truth to it.

3 - More an argument against floating bridges. String changing is more difficult as the whole instrument goes out of tune, but not locking the nut down will make no difference to this. Also, what would you be doing playing a show with only one guitar resulting in you having to run off stage to spend 10 mins changing strings? Always have a backup....

4 - You don't suddenly run out of rope on a fine-tuner, so you just need to be aware of what you're doing and take action ahead of time.

Sounds like maybe this guy just doesn't like the double-locking type of guitar which is fine. It might be better for him to say 'If you're starting out, buy a hardtail guitar', which is also reasonable advice - less to worry about etc. I can see no reason to have a double locking guitar and not lock the nut - the only time I don't do it is on one guitar where I play with the tuning so regularly that it doesn't seem worthwhile. I take 3 guitars when I play live, sometimes more so I can just swap and carry on, but in all my years of playing I've only once broken a string during a show.

Buy a double locking guitar and double lock it, or don't buy one... I can't see the point in going down the middle road. Ask your friends why they do it, I'm curious :)