The benefit is that the impedances between the two components will be corrected. The drawback is that the Burson introduces some gain and may introduce unwanted coloration. Hard to tell if it's the dream fix without trying it. Anyway, $550 new, can probably sell it for $400 used. Not a bad experiment given that there seem to be few other options.
My personal opinion: You would be nuts to give up that lovely SET sound. Although perhaps there are other 845 based SET amplifiers that have a higher input impedance.