I have one for my 4550 and it makes the image really bright but I haven't tried printing 35mm with the 4x5 mixing box for comparison. The times I get for an 8x10 with the attenuation filter closed and the lens set to f/8 are in the 8 to 12 second range with dichroic filtration on max magenta or yellow (that is a combined time). I also have to set the lens to f/8 for smaller prints otherwise I don't have enough time to dodge anything. At full extension of the head I get times of 12-15 seconds at f/5.6 with the attenuation filter open. These times are on VC papers such as Oriental.
The one caveat I would add to this is I don't know if the little condenser on the 35mm mixing box is large enough to use a wider lens like a 40mm for example. I have been meaning to ask here if anyone does it. I usually use a 65mm for enlarging 35mm though. I get perfectly even light with a 65mm. A 50mm still works fine but needs to be more carefully centered. (I use the 4x5 glass carrier with a home made mask for 35mm).
I hope that helps.