Hi J.,
We bought a toddler bed for my son when he was 18 months old and he was fine in it. However, we did find it to be not worthwhile as it was the same size as his crib and he really didn't seem to get any benefit out of it. He transitioned to a twin bed at 2 1/2.
He did slither out a few times, but he never "fell". We just put a futon down next to the bed just in case and sometimes he would be on that in the morning, but he never cried or hurt himself or was scared in any way.
We now have bunk beds. For my daughter, we decided that the toddler bed was not worth it and put her straight in the bottom bunk at age 22 months. She has never slithered out once and there is no rail. (Put the futon down - was never needed).
She is now almost 3 and her friend at daycare who is one week older than her - is still in a crib. HER Mom wants to keep her there as long as possible because she doesn't want her getting up in the night by herself.
I guess those are the things to consider:
Does your daughter wake up much and will she be safe wandering to your room, (can she open doors etc)?
Does your daughter move around a lot in her sleep? Might she slither out of the toddler bed?
If she's outgrown her crib, has she outgrown a toddler bed already? - because they are exactly the same size.
(If you get one - don't buy a mattress - you already have one!)
Toddler beds can be fun, if you buy one with a cool design, but I have another friend whose son had a hard time transitioning out of the "Thomas the Tank Engine" bed
because he loved Thomas. By this time - he REALLY needed to be in a bigger bed and it was quite traumatic for everyone with sleepless nights etc because he was too attached to "Thomas".
Hope this helps.