I don't have any experience with products from RTE. Like you, I find them the most advertised all over the interweb including this forum. One of the reasons is ease of installation. It will plug into the back of a standard inst' panel just like OEM.
A product called "meter match" was very popular also but as time goes by other mfgrs offer pretty much the same products at a wide range of prices.
If I was seeking a solid-state gauge voltage regulator, I would just search that at ebay. Any will work if wired into the circuit properly. It doesn't absolutely have to be located on the back of the inst' panel. With a little longer wiring it could be placed anywhere under the dash.
If the IVR4 still has the flashing LEDs on it (which surely contributes to its cost), wouldn't they be more useful if located where they can be seen?