Quote - I read a lot of mentions about weight mapped V4.

How is it better than plain V4 or V4.2? 

Can I use it with existing morphs and clothes?

If I have a dialed V4 or V4.2 character can that be applied to a weight mapped V4?

Is it easy to use?

First, weightmapped V4 bends much more naturally.  Especially without all those add-in morphs and magnets. 

It's better because everything about the model is more like a natural human being.

All existing morphs and characters work with V4WM the same as V4.2 - nothing is different.

Clothing will need to be converted using the FREE Outfitter from PoserPlace so that it is weightmapped.  The conversion process is simple and easy and transfers morphs, movement bones and everything else to weight mapping.

Shoes and hair are sometimes iffy and will simply need the Edit>Copy Joints from Figure to allow for a better fit on a weightmapped V4. Those are both hit and miss and will simply require you to test and determine which is the best solution.

I believe you can weightmap your morphed & saved V4, but I'm not certain.  Since both scripts are free and easy to use, with lots of documentation and help here and at Poser Place, I'd suggest trying it and asking questions if you have any problems.

You may have to weight map a"plain" V4, then put your morphs back in, then save with your morphs applied.