I've been daily driving the RSX for about a year or more. Unfortunately I haven't been able to do any other modifications due to time constraints.
About rubber. If you make engine mounts with rubber, you can't really replace them easily unless you made them a press in like we do with the urethane. And if you're doing that, urethane is a better choice.
Hard Race probably uses an Asian manufacturer that basically copies the Honda mount, which means the rubber is bonded to the steel case. There are several of these manufacturers and they sell mounts to companies like O'Reilly, Pep Boys, JC Whitney, etc. Back in the 90's when we owned a salvage yard and sold aftermarket copies of stock Honda mounts, I noticed they were much stiffer than stock. Hard Race states their mount is 150% stiffer than stock. They may specify a stiffer rubber when having them made, or they may just come that way from the manufacturer. But if you decide you need an even stiffer mount, you're out of luck. So if that was us, we would have to stock more part numbers to get the range of durometers we need to satisfy our customers. By having replaceable urethane, we stock fewer parts.
Also rubber eventually tears and if it's bonded to the steel, then you'd need to replace the whole mount. It's much more economical to just replace the urethane. We also have the option of changing the durometer if the problem is being caused by too much horsepower.
brian g