Saws aren't exactly a Leave No Trace tool and should be used with much discretion. Turn the uninitiated loose with one and you may have some ugly campsites.
The TOPS saw is just a Saws-All type blade in a Kydex handle. You won't want to cut much with it. The pivot point will fail with extended use.
I think saw have great value as a survival tool and are handy for sea-kayaking where you can hack on driftwood. I could see using one if you have a wood stove, but most stoves use small diameter fuel that can be broken up by hand. They are probably best for car emergency or earthquake/storm kits.
The Gerber Sportsman's Saw is a little over 3oz and is the lightest *effective* saw that I have found. The Kershaw folding saw (same as the Bahco Laplander) is stronger, but double the weight. The Gerber will cut well enough that you could get enough wood for a shelter and a survival campfire. They are a good buy at $10-$12.
If you just want to cut branches to hold up your tarp or a hiking stick, the saws found on the Victorinox and Wenger Swiss Army knives will work fine. You wouldn't want to do a lot of cutting with any of them, but the larger ones can do some real work--- the handle is the thing. You do get the handy-dandy knife and other tools along with the saw. Most are in the 3-4oz range.
Models to consider:
One hand opening Trekker (largest/heaviest)
Farmer (coolest, with Alox scales/handles)
Hiker (like the Farmer, with a thinner knife blade and plastic scales)
Fieldmaster (adds scissors and more)
Huntsman (like Fieldmaster, but has a corkscrew rather than a Phillips screwdriver)
Several in the Ranger series, with long blades-- bigger than the Victorinox 111mm models (spendy and harder to find)
Handyman (like the Vic Fieldmaster)
Several of the Evo series (techy look and fairly expensive for an SAK)
Leatherman makes a few tools that include saws, but the weight is out of bounds for most UL hikers. The Wave is a wonderful tool, but an anchor at 8oz. IMHO, the saw isn't any more effective than the one on a 3oz Swiss Army knife.