Fast forward many months later.
I picked up a cheap white RF only PC engine, and decided to look for a cheap AV boosting solution.
http://www.ebay.com/itm/PC-Engine-AV-Booster-RGBS-output-TurboGrafx-16-Composite-RCA-RGB-SCART/152642002285?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649And it looks like Justin Choi put up a newer revision of his AV booster. It arrived yesterday and while it's a little flimsy, has no outer case, it works pretty well for the price. With a cheap 5.00 Genesis 2 SCART cable I didn't notice any major problems with either the sound or the image over SCART. I also tried a nicer shielded SCART cable with more or less the same results.
Obviously, Mickcris's RGB moded Tennokoe II produces a better image, has an outer shell and is a much better overall product. However, if you're just wanting a cheap solution to improve the video from an RF only console this isn't a bad product for the price.
I don't have one of the DB elec boosters to compare the results there, but if you're just looking for a cheap solution with decent results this isn't a bad option. If you're looking for quality + saving, the modded Tennokoe II is clearly the way to go.