I have the newer Lowepro Slingshot Edge 250. It feels ... big, but not unwieldy; is very well-padded and protective of gear.
If you're used to traditional camera backpacks, the fit and drape takes some getting used to.
The main compartment takes a mirrorless with larger lens, extra lenses, hoods, etc., and is more commodious than it looks.
I have had a second small mirrorless in the upper (laptop) compartment and have carried point-and-shoots and flashes in there. Padding is not as robust as the main compartment, and I wrap delicate gear carried there in small Tenba velcro "wraps."
There is no lack of space for smaller ancillary kit. Haven't tried carrying a tripod in the compression straps, nor a water bottle in the mesh pouch, but my thought is that the whole may feel "unbalanced" at one side if that much weight were carried. Maybe the designed load capability is a little contrary to the portability-easy comfort spirit of a sling bag
The crossbody strap works - one might wish it were a bit wider - but it is fiddly to retrieve and stow away.
Extracting gear while wearing the sling took me practice to achieve, ah, unfumbly grace and surety of movement, but ya can't go by me. Not yet sure that it's any more efficient than a smaller traditional two-strap pack. Time will tell.
Definitely the kind of thing that takes an in-store "try-on" - the idea is appealing but it proved (to me) a totally different feel in use that you may or may not like.