Att s1? What’s so awesome about it? Never heard of it- all I know of are the RR, Merkur, & ikon.
A little mousing around on B&B will fix that!
Tooting my own horn a little, look for "The Tilted Picnic" which is a series of slant reviews I've done for the last three years, so far.
There are other threads about slants all over; a simple search should turn up a couple hundred at least. Also, read in the Brotherhood of Slant Shavers (BOSS) subforum.
To your question: the ATT S-series slants (S1 SB, S2 OC) are an innovative take on slant design. I have an S2 and it's been my favourite razor for years.
It's a good time to look into slants. RazoRock is bringing out a whole new line of them, Above the Tie has the S and X series slant razors, Phoenix Artisan Accoutrements has the whole Monster series as well as the Filament and still some of the Alpha Ecliptic left I think, and there are plenty of other slants out there to explore.
In the vintage line there are many European slants (Merkur, Fasan, Globusmann, etc. etc.) and even some of the more recent "vintage" like the RazoRock Stainless Steel Stealth Slant (a Globusmann copy) are still fairly easy to find. Also the iKon Shavecraft 102 which is a tilted slant instead of helical but a very good shaver nonetheless.
Even the Gillette guys get a slant! There's the "Wanton Destruction" slant, "re-made" from a Gillette.
Lots of room in the rabbit hole; c'mon in!