Interesting aluminum bronze adjustables. Those are made specifically for non-sparking applications. However, aluminum bronze is 95% as dense as steel so there will not be any noticeable weight savings.
As for what the OP is asking about I would go with Lobster as they have removed lots of weight in their design. Like this...
http://www.ebay.com/itm/like/121524606537?lpid=82&chn=ps&ul_noapp=true
LOL. Yeah, not only is aluminum bronze just as heavy as steel, it's also MUCH softer.
I saw the Lobster adjustable wrenched on Amazon. The reason I didn't recommend it was that the reviews said it wasn't all that much lighter than an ordinary adjustable. That was why I mentioned "speed holes".
I was able to find some mega bucks titanium adjustables, but nothing with steel jaws, and I would expect the jaws to wear out quickly if used on steel parts. An aluminum AN adjustable will probably be permanently damaged on the first use on a steel nut, while the titanium will not, but I still wouldn't expect a lifetime of use from one, so again, no recommendation.
Ridgid does make smooth jaw pipe wrenches (they call them hex wrenches):
https://www.ridgid.com/us/en/hex-wrenches
but not in aluminum. Sorry.
Looking at their design points something out to me. You cannot simply grind the jaws smooth on a pipe wrench and expect it to turn nuts (there's too much slop in the jaw, by design). By only contacting two flats, it is doomed to failure (monkey wrenches remove this slop, but I don't see these in aluminum either). The Ridgid design has a hooked jaw that contacts two flats on its own to avoid the problem. It looks like it might be possible to put one of these jaws into a Ridgid 45 degree aluminum pipe wrench, and grind the handle jaw smooth to make a lightweight version of this. Though it would be expensive, and I don't have any idea how well it would work.
If you go this route, I think a slight cylinder bias on the handle jaw grind would help with off-edge engagement.
The recommendation by PureLeaf to go with a Knipex Plierswrench may be the best one for you. I'll see if I can get pictures of my 12" PW next to a 15" adjustable. The only thing you lose is 2" or so of handle length for extra leverage (you don't get much leverage from the last inch of an adjustable where the end is rounded off), BUT the PW grips the fastener much more, so is less likely to round thing off when really torquing stuff.