The MNP Track cleaning car (HO):
I wanted to see if I could use the felt pads in conjunction with Flitz metal polish for periodic "deep" cleaning. I don't like GooGone or Aero Locomotive track cleaners for the reasons below. My only problem with Flitz has been that it is difficult to apply it with a cloth and not get any on the rail sides where it turns green over time. It can be removed with a stiff paint brush, but I'd rather not have to do that. Flitz cleans so well that I've used it anyway.
But back to the MNP car: It works! Since Flitz is non-toxic (USDA approved for food service), it can be spread on the felt pads with fingers.
Just put a small dab on the pad and spread it on so that it there are no globs left on the surface. The PULL the car SLOWLY over the section of track to be cleaned (that way, the locomotives wheels don't get any on them. There trailing wheels of the MNP track cleaning car will get some). One application does about 10 feet of track, maybe more. You can continue to reuse those pads as Flitz applicators until they wear out. It would be good to have second set of rubber discs. You only need to make a single pass over the section to be cleaned.
Wait about 10 minutes for the Flitz to work.
Then change pads to plain felt ones and PUSH the car SLOWLY over the same section. Again, push the car so that the loco wheels only go over cleaned track and don't pick up any dirt. Note that even if they do, it is Flitz dirt and will be easily cleaned off of the wheels as you would normally do a wheel cleaning.
I made about 10 polishing passes over the test section which was pretty dirty. The rail heads looked like they were plated and no more Flitz came off on a clean cloth. There was NO Flitz residue on the sides of the rails or anywhere else.
Note that once the Flitz is applied with the cleaning car, it would be faster to use a shop cloth (one of those red cloths one buys for use as rags for automotive work: they have NO nap) wrapped once around a wooden block to polish the rails where you can reach them.
My take on this is that the MNP car does the best job I've seen of applying products like Flitz (MAAS metal polish is also reported very good, though I've not used it), and then maintaining the rails in top condition between re-applications (every three to six months; even longer if I keep my grimy fingers off the rails :-).
I like Flitz better than any of the GooGone or AeroLocomotive Cleaner products because:
There is NO "conductive" or other residue which you can feel left on the tracks. GooGone leaves enough behind that plastic wheels can be affected by it.
Flitz is NON-TOXIC. You probably shouldn't use it like mayonnaise, but it is USDA approved for use in food service.
It leaves an anti-oxidant bonded to the metal. It is conductive and I can't feel it with my cloth or fingers. I think it just wears out after a while, but the rails stay CLEAN and shiny.
For the record, I have NO interest in Flitz or MNP; I just use their products.