There is absolutely one pencil kit on the market that is better than all the other ones! It is the so-called Perfect Fit Convertible pen/pencil that can be had from Berea. You can use it either as a pen or change the insert (refill) and use it as a pencil. The mechanism is made by Schmidt-Germany and so are the pencil inserts. I think a insert is somewhere around $3-4 and can be extra purchased. This is a great way to offer both, pen and pencils without making them dedicated when you turn them. A similar pencil is or at least was some years ago available from Woodcraft, using the same mechanism.
So far all my experience with pencils have been not very good - most of them came back for repair or exchange to another pen. The clicker mechanisms seem to give up pretty fast and the other type, the twist-type where one has to feed the new lead from the front are pretty awkward to use, i.e. refill a new lead.
PS: just saw that some pencils from CS are also utilizing this type of pencil mechanism.
Rudy