The problem with modulating the gas but not the air is well documented. Every one I've ever seen was really crud died up inside to the point that the HXer had to be pulled out to be cleaned with a pressure washer due to accumulation of corrosive byproducts due to condensing.
Looks like a real great idea on paper and in the labs, but doesn't pan out well otherwise.
In order to have complete and total control you MUST be able to control the flow of not just fuel, but also primary and secondary air. Skip any one element of control, and the equipment will suffer.
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
For a large 4 zone residence, I specified a Thermal Solutions Evolution copper tube non-condensing boiler several years ago. The convector style pretty much assured that we would need 140 degree water anyway.
It has a hi-low ceramic burner, ODR, adjustable curves, etc. Everything still looks great on it. Combustion has stayed in adjustment remarkably well over the last 4 (I think) years, only it requires a yearly combustion air filter change. It's just that I think 500,000 btuh is the smallest they make.
Also, it's not inexpensive. But very lovely nonetheless!