hey T.!
i agree with sara's response. if your son is showing all the signs, go for it! he'll let you know if he's not ready. with both my son and daughter, once i started the training process i didn't let them use diapers or disposable trainers at all. if you take them out of the diaper they are more aware and tend to adjust quicker. my son was accident free from peeing within four days and sleeping dry through the night. pooping took a bit of work because he was a private pooper. i had to really pay attention to when he was playing behind the couch or wanting to be alone in his room. that took about 2 months before he was completely accident free. he was 2 1/2 when we started.
my daughter came to me on her 2nd birthday and said she wanted to start using the "potty" and never had an accident. (i know, rare case!) we had been getting her used to the idea for about 3 months before her birthday. she'd sit on the fisher-price potty that talks to you and makes flushing sounds and she thought it was so funny. she never really used it other than to play with because she wanted to use the real toilet like us right away.
also, this is a great time of year to start training because the weather is (usually) so warm. if you are comfortable with this, you could let your little guy run around bottomless for part of the day especially if you are playing in the yard.
there might be other moms who were successful with the disposable trainers but both of my kids treated them just like diapers. i think the clerk had a good suggestion in using them at night just to make sure your son doesn't wet the bed. if you see that he is staying dry all night, take them off.
hope this helps. good luck!
K.