All three are different, so it’s best to decide what you need and what you want to do, and then buy the product that does it.
The BeeDrive is the most different, because it’s just a USB-attached SSD with special firmware and software. The USB interface makes it about 4 or 5 times faster than a regular Synology or the BeeStation, but it’s also not standalone.
Both the BeeDrive and BeeStation offer specific features, no more and no less. A Synology NAS is a very configurable, flexible system. It costs significantly more but you can add/remove drives and configure the software in all sorts of ways; it will do just about anything you imagine, although it’s not a slick, plug and play setup like the Bee products.