If the Invisibrake system is in fact a progressive braking system as opposed to a proportional braking system, ...
Second FAQ: https://www.roadmasterinc.com/produc...rake/faqs.html
As I noted before, good enough seems to be good enough. The only people I've read that complained about the toad stopping the motorhome or the toad's brakes locking up had a misadjusted system of any of the three types, proportional, progressive, or surge.
Actually, I've probably read more of those posts from people using the ReadyBrute/ReadyBrake than others due to the mechanical cable dragging or binding up due to lack of maintenance. But it's still just a few.
Others have been from a portable system where they fired up the car and then forgot to bleed the stored-up vacuum off before towing.
I do not recall ever reading about the problem with an Invisibrake or Stay-IN-Play DUO.
The Stay-IN-Play DUO also taps into the vacuum booster line on the car, the same as the Invisibrake. The installers I had quote the Invisibrake said their pulley arrangement added needless complexity to them and increased the install cost. I dunno myself.
The Stay-IN-Play DUO uses a similar actuator arrangement clamped to the brake pedal but it anchors directly to the firewall in front of the brake pedal.