we used some in the last org i worked for, had a few of those and other kinds. I think you want to look at the accuracy specifications to make sure you understand if they meet your accuracy/precision requirements and that they'll work with the software you intend to use for data collection. My recollection is that accuracy was the biggest issue, they just don't provide the accuracy other solutions like Trimble offer, and they may not be able to acquire signal in challenging terrain and canopy the way other GPS receivers do. The biggest thing is making sure you know what your requirements are and if a given product satisfies those.
