Hi Hondaking,
I purchased one of those zinc kits of ebay about two years ago when I was restoring my CB650Z.
You need alot of patience and determination if you want to get good results. Everything has to be spotlessly clean before it goes into the zinc bath. You will need to replace the chemicals and the acid after a certain amount of use to maintain the quality of the zinc plate finish and you will have to replace the zinc anodes as well as they just dissapear into the bath (onto the metal).
If you put in a nice smooth peice of metal you will get really good results, so it depends on the condition of the metal. Any metal that has rusted, even though it may even be sand blasted will have pitting and will not look good. Some metal, (alloys) will not take a coating of zinc.
I reclaimed a lot of parts when restoring my CB but there were some parts that were just not good enough to put on the bike even after zincing. For the cost of the unit I could have replaced a lot of metal parts NOS.
Best way to describe it is a love hate relationship. You need a lot of determiation for it to work out.
Would I buy another kit, in a word, NO.
Hope this helps.