I don't use them because Zane genuinely behaved worse when I put them on him than he did normally.
That being said, I think it is important to try anything that may benefit your child's safety!! Only you know your child well enough to make that decision!
Zane was about 14-15 months when I started letting him walk out and about in the town, I bought a wrist strap for the day when I decided to do it, and used this for a couple days while I ordered a set of reins off ebay.
The wrist strap was a complete success, I taught him from Day One that he is to hold my hands at all times and used the wrist strap only as a way to let him explore those couple of extra feet away when something was particularly interesting to him (like stones, flowers etc).
The reins, for us, were a nightmare! He liked putting them on just fine, but it took him all of 2 days to realize reins meant he could run forward a few steps and before I could loosen the slack again the reins would pull him back down and it was a "great game". He would just pull and pull on them testing us all the way refusing to hold hands etc. Yet take them off him and he would cling to my hands like we were glued.
To be honest, Zane has always been a good, calm boy really, and combined with teaching him "Wait" as his first outside command I NEVER had a problem with him running off or showing any interest in being more than 2 feet away from me. Now he's 2.5 he will run up the street about 10-15 feet maybe before turning round and telling me to hurry up lol but when we start approaching the area of town where there are several crossings in a row, he always comes right back to me and tells me to wait for the green man =P
For my family, reins haven't proven to be worth it, I will probably use a wrist strap for the first few months of walking with number 2, But if he is as calm as Zane always was then I'm hoping it won't have to be for to long. If he is an active child then I will keep an open mind to reins etc =)