I installed 1 a year ago and here are some observations:
1 - You will need a 17mm allen wrench attached to the largest leverage bar and a whole lot of muscle to break the factory plug loose.
2 - The heater will need some good thread seal, mine leaked the first time I installed using the teflon tape.
3 - The cost of the heater was $55 with shipping from Carver.
Again, the hardest thing was removing the factory plug. Good luck.