Rayox DCR250 actually is better than the closeup filters because it has 3 elments compared to the single element close up filter.
Like I said, for ALL closeup filters, the DOF is going to get thinner once the zoom becomes longer. The only issue is how much thinner it is going to get and when it gets unacceptably thin.
The only difference between a +4 and a +10 filter is the magnification you are going to get at the SAME zoom. A +10 filter is going to give u much geater magnification at ALL zoom ranges.
The +10 filter can be used on your 18-55 kit lens whereas the +4 filter won't give u much magnification if used on the kit lens.
Stacking the filters is not recommended espeically for single element filters.
Anyway, I have a set of +1, +2, +4 and +10 filters for the 55-250 lens. If you are free, you can join me on one of my macro outings to test out the filters on the 55-250 lens.