A few days ago we featured a new speedbooster adapter from Fotodiox, the Excell+1. The idea behind the booster is that is remaps the image crated by a full frame lens into a smaller sensor, thus both un-cropping the image and gaining a full stop of light.
Now, this is not the first speedbooster that has gone to the market, about one year ago Metabones introduced a similar series of speedboosters, but the pricing on the two products varies significantly. An Excell+1 would set you back about $160 where as a Meatabones adapter will cost between $490-$590.
Videographer Max Yuryev took the two adapters for a ride and the results seem pretty conclusive to me. You can watch the video above and make your mind alone.
The test used three lenses shooting a piece of printed journal: A Sigma 18-35 1.8, Rokinon 85mm 1.4 and Tamron 17-50 2.8. Max puts all the lenses at their widest aperture and then adds a stop using one of the speedboosters. One option is that Max got a lemon copy of the Excell+1 but if not, Fotodiox should probably go back to the drawing board.
I grabbed on image from the video to give you a general idea, but I recommend watching the entire thing to make your own mind.