I'm going to answer this by going more Slim vs. Fatboy, since the Toggle is closer to the Fatboy than the Slim. Acknowledging the difference between the Toggle and Fatboy (weight, balance, difference in moving vs. bending the blade on adjustment) they both have a very close feel and effectiveness with each other. The Toggle comes across as a bit more aggressive, but other than that they're about the same.
The Slim is the lightest of the three and has a different head geometry. I found some pictures that
@Jayaruh shared in 2016 that help see the difference.
I shared that information because I think it explains the difference as I experience it. My own experience is that the Slim is easier to maneuver (probably due to the longer handle and difference in weight, as well as the slimmer head) and doesn't feel as aggressive as the Fatboy. An example is the fact that for the past two nights I've had the Slim on 9 - my namesake setting - and have gotten absolutely irritation free, smooth and wonderful shaves. When I go 9 on the Fatboy or Toggle I get great shaves but I run into some irritation, even if it's light. It just seems to me that the Slim is a bit milder across the board.
Since I don't shave my lip or chin I can't speak to the handling of the slimmer head vs. the larger head of The Fatboy/Toggle, but I have seen a lot written about how much easier it is to work those areas with the Slim.
Are we on the same page? Oh, and to answer the obvious question at this point - which razor do I prefer? I would say the Fatboy first, the Toggle on performance just a hair under the Fatboy, but on coolness factor it would win, then the Slim. But the preference is tiny. My reason for preferring the Fatboy has to do with my preference for aggressive razors over mild in most cases. Its styling just looks a bit cooler than the Slim as well. Boy, am I superficial or what?!
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