Depends on which one.

One is just a resistor in a nice housing. Totally not worth it IMHO. I build my own discharge banks and will likely start selling them soon.

The other part they make is a full regen setup and if they weren't so expensive, I'd get one. With the regen setup, you can use both ports on your 406duo to cycle batteries at 40 amps using the regen feature. They did a little work to get the charger to work with both a battery and a power supply.

The main con is that it'll cost you $350-$400 USD to get one from them in france. The US side isn't importing them. For that kind of money, I could buy another icharger and discharge bank. They're also heavy because your carrying a battery around with you. You do need to be aware of the battery state of charge and make sure you put the regen battery into storage mode at some point.