Tons of posts on this forum that mention Clipper Creek, Chargepoint, EVGo etc etc etc, but you can't mentioned this one?
So not knowing which product you are discussing, let me tell you my experience with my 13 Chevy Volt.
I purchased the EVExtend kit and installed it myself.
This kit allows me immediate access to the 12v battery through Anderson Powerpoles to a 1,000 watt 120v AC inverter. I strung a 100' heavy duty 120v extension cord from my garage to have immediate access to my kitchen refrigerator and some lighting when needed in an emergency.
When my lease was about to end, I personally removed this kit and it collects dust in my garage (eBay soon maybe).
I have considered their newly announced product for the Bolt EV, but given that my lease expires in 11 months, I will probably not purchase it unless I purchase the Bolt EV at that time.
This product makes it easy to connect and disconnect from the 12v system and I feel is worth the cost.
I also used it to power my portable amateur radio system when I used to take it all in a backpack with a portable antenna system up to mountain tops for an afternoon's enjoyment around the world on the radio.