The focusing distance when using the Close-Up filters are :
Focusing distance = 1/Dioptre (in metre)
For eg...if a close-up +4 is used, the focusing distance is roughly 0.25m.
The Hoya close-up filters (esp. +4) is good enough for most macro work esp. flowers, butterflies, etc. Hoya does make a +10, but I reckon focusing is difficult as the DOF may be a little too shallow. I tried with 2x +4, and there's almost no way I can shoot handheld. It has to be mounted on a tripod. The Hoya's are cheap, about S$20 at most for 55mm thread.
For best quality, try Nikon 6T or Canon 250D macro lens. Very minimum distortion and aberation, but much more expensive.