Yep fast fret and stringez, are nice. If you look at the ingrediants,, it pretty much just mineral oil,,, So if you want to save yourself some money,, get a bottle of MO and a nice chammy. you can clean strings and fret bd at same time.(mo on mo off with seperate cloth.) if you want the lemon smell,, get a bottle of essiential oil lemon and put a coupple drops in.
Fast fret is preinpregnated cotton wadding with MO and string ease is MO with a little sent added.
I have looked up a few different guitar care sites. it is almost an even split between mineral oil and pure lemon oil. I have been using either or. Have not noticed anything that would be called detrimental.