Does anyone have experience using the Will forms that are found on web pages?
Yes.
Are they complete?
Not always.
Are they legal?
The only way that can be determined is, after you die, the documents are presented for probate. The court will then decide whether they are legal or not. If not, then your assets will be distributed as if you had no will.
I assume once I complete and print it, I need to file it at my local courthouse?
Normally wills are not filed with the probate court until you die; some states, however, have provisions of keeping a will at the probate court without doing anything with it till you die and your heirs then file it and start the probate proceedings. I don't know the law on this in your state.
Can it be used to supersede an existing Will?
If worded correctly.
When you use home-made wills, you are possibly creating a can of worms which, when opened, will multiply and soon inhabit the earth for many generations to come.
If you have any assets that you want taken care of and potential heirs you want to take care of, then go to a lawyer.
If you do not have any assets that you want taken care of and potential heirs you do not want to take care of, then use online will forms.