You can get the cheap one and risk burning your house down or having an expensive paperweight.
Evolve used to sell a 2A version that is equally as good, and slightly cheaper, but they don’t carry it any longer. Metroboard has a 2A one but it isn’t the really good one.
Sometimes if you’re way out of balance on a very large P-count pack you might want it to stay connected. Most of the time it’s better to disconnect.
You can plug a voltage gauge into the charger and watch what it does
Some just go straight to 42.0V, some turn on and off and on and off until you plug into a battery, then they start charging. Those are the better ones.
Here’s the model number for said enertion charger above,a simple google search brings up plenty of results,you can get one off Alibaba for $40,just make sure you set it to the correct v for your country before you use it!
P/N:EMC-180