Basically, unless you are absolutely sure the tung oil product that you are buying is pure tung oil there is virtually no difference between the two. Pure tung oil will enable you to put a nice finish on the piece but it will be a relatively “soft finish” . But most “tung oil” products that are commonly available are simply tung oil (about 20%) mixed with varnishes to harden the finish coat and mineral spirits. Check the label. If it states that it contains petroleum distillates then this is simply a wiping varnish and not 100% tung oil.
There will be no difference between finish coats of polyurethane and a tung oil/varnish combination. If you decide to go with the poly I would recommend using a wiping poly. It is the more forgiving than poly right from the can. And save yourself some money by making your own wiping solution. You can make your own by simply cutting concentrated oil base polyurethane to 50% concentration with mineral spirits. You will have to put on more coats of the wiping product as compared with the concentrate to get a similar film thickness but the wiping poly goes on much faster, is self leveling, dries quicker and less prone to runs and sags. Just apply it with a clean cotton cloth or paper towel by wiping it over the wood surface.
-- With God's help all things are possible- even woodworking. Woodworking is not just a hobby, it is an (expletive deleted) expensive hobby.
