I didn't try it on my beater. I use it on the Bullitt. I have a private well for my water here, not filtered, and this thing works just as advertised. What you might not be aware of is that this is a single hand-held plastic unit that attaches to your hose, and the soap goes in the reservior, and the filter goes in it's niche, and you use the three-way dial to select the rinse, soap, and dry. Since the Bullitt is black, any spotting is horribly obvious, and the Mr. Clean does a very good job of preventing that. Of course, it isn't fool-proof; if you have water dribbling out of the crevices after you've washed it, you'll want to dry those off, and not leave it. It's also a bit awkward to use the hand unit. It's bulky, and the hose coupling doesn't swivel as well as it should, making it difficult to use with one hand. I think it might benefit from a whip connection with a better swivel (read: not plastic). Also, I prefer to keep the sponge in hand as I go, and you pretty much need two hands to switch from soap mode to rinse. As far as the soap and filter go, they recommend that you don't use any other soap but theirs, because it will clog the unit. I haven't tried any other soaps; if it ain't broke, don't fix it, as they say. The filters can be bought locally here for just over $5 apiece at WalMart, and 20 oz. of the soap is just over $4. The filter that came with the kit is supposed to be for 3 uses, but unless it turns brown, it's supposed to still be good. All the regular rules of washing a car still apply: don't do it in full sun, don't do it if the car surface is too hot; don't let the soap dry on the car. If you have water spots already on the car, you'll need to remove them first, and if you get rained on after, you can expect the same results as you always get when your car gets rained on and you can't dry it right away. No magic there.
I'm thinking that, for the sake of convenience, I'm going to try using the soap in a bucket, and use a conventional spray head for the rinse and after that, I'll switch to the unit for it's filtered dry. But as far as the product goes, I recommend it. It isn't often that you come across something that does what it's supposed to do, but this does. Amazing.
Oh, and just a side note: when you buy the kit, read the literature that comes with it. The enclosed f.a.q. is pretty funny, and from it's tone, I think a car guy (or gal) wrote it.