Thanks for the reply. I just feel like I am missing something.
This system seems cheaper (one less temp controller, one less burner, no need for plate chiller). No risk of scorching my mash. So why are there so many clones of Lonnies system?
What are the cons to this system compare to the Brutus 10?
I think the reason for the popularity of the brutus is the combination of it being a great system and the detailed plans being widely published. That doesn't make it the best sytem for everyone though.
IMO the main advantage it has over HERMS is the speed at which the temps can be raised for step mashes, mash-out, temp corrections, etc. Even though the original Brutus calls for two pumps, it can be built and operated with only one. A HERMS requires either a second pump or a stir mechanism to circulate the water in the HLT. Another advantage of the Brutus for the less DIY inclined is the availability of detailed plans and easy to follow instructions. And FWIW there's really no risk of a scorched mash with the Brutus unless the pump stops working and you fail to notice it for a while.
While the HEX in a HERMS can be used for chilling, it's not always the most effective or efficient method, which is why many HERMS owners use other methods to chill. My "cold" tap water is often in the 90's(F), so I'd need to recirculate ice water for chilling whether using a plate chiller, IC, CFC, or anything else, so using the HEX as a prechiller with water and then as a chiller with ice isn't much different than any other system for me. If I had cold tap water, I might not use the HEX to chill, or if I did it might be as an IC rather than running wort through it.
The reasons you mention along with my water situation are what pushed me towards a HERMS, and I don't regret it at all. Good luck with your build! Come back with any questions you have along the way, and be sure to post pics.