The original (20-year old!) heater was still working until I installed a temp sensor incorrectly and accidentally dry-fired the heater. So I was very pleased to find this unit with a Hi-Limit Sensor included for the price. The one thing they don't say in the instructions is that the new high-limit sensor isn't supposed to seat all the way in as the old one does. But SpaDepot's support was great. They confirmed that it just needed to be caulked with some silicone to hold it in place. (See pics: old heater/sensor on the left, new units on the right.)
And, many thanks to John Reihing, who described in his review on this site how to keep from dry-firing it. Because of him, I was able to self-install with confidence.

Good price and quality. The install wasn’t too difficult. The only problem I had was the two wires that went to the circuit board had a connector on them and I needed them separate so I could just plug them in the back of the existing 14 pin connector. The heater getting power indicator was a nice new feature that I didn’t have before.

Fit 2014 Sundance 880 Marin perfect. Took 6 hours to heat from 51f to 89f.

I have a 2019 optima 880. This heater was a perfect fit. Installing it was a bit trickier than what is in the video and comments. I needed an 11/32 (i think) wrench for the ground, my ground post spun with the nut, as did the heater posts. The vice grips only slowed the water leakage….. things were a mess. The upper heat sensor wires did not fit into the plug all the way so they were not making contact with the main board, i ended up removing the unused locking shroud. All in all it was a 1.5-2 hour job, start to finish. I will do this again as needed, i would just overprep before starting..

Ordered the heater after oem unit finally died after 20 years. Very easy install when following instructions and very glad they gave some new hose to connect both sides. Really like the additional indicator lights. Works just like clockwork and heats 5 degrees per hour.