I wouldn't recommend a 2B if Cock Hero is what you want. I suggest building your own DIY unit for less money, it's what I did and it's pretty much just connecting a bunch of wires together to the right stereo amplifier, then to a resistor and audio line transformer for each channel. Cock Hero videos sometimes rely on phase shift audio at frequencies that the 2B doesn't handle well which usually gives an unstable volume level or it turns it into a lower volume or just a buzz feeling which can be unpleasant.
Let's say I didn't want a DIY unit, the BT Stim is essentially the same thing(it's based on an audio amplifier) built by someone who has built a pile of them, there are shipping delays on these right now due to COVID causing the person making them to have delays on receiving some of the parts he uses for his design. The ET-312B is an order and wait situation right now too, but I don't know the story from them but last I checked their web site says it's backordered, check with them before ordering. Out of all of the non-amplifier devices, I think the ET-312B is the best. If someone asked me to try any estim device that I haven't already, I'd want to give the ET-312B a shot and this is mostly based on people who I know have tried the analog devices(DIY/BT Stim), ET-312B, and 2B. It seems people who have tried multiple devices land on DIY or BT Stim devices as being the best.
Here's a link to the most recent Milovana Estim Device thread, you can read through people's opinions on devices including a few that have more than one and you can read about compatibility too.
viewtopic.php?f=12&t=23154
