I prefer the egg yolk lecithin for main use. The only thing I really use the Vets-Best for is incentive dust. Well sometimes Queen Eva gets a whole tablet crushed over a couple of meals (one tablet spread out I mean) if I think she needs a little more help, or if she's had a lot of bone (which can constipate) But I'm really happy with the egg yolk lecithin.
Mazy (SK) gets a whole capsule daily of the Nature's Plus, half in the morning half in the evening, I give it with a first meal, when the stomach is empty. The other two get a half capsule every other day, (they get the Swanson's Brand) also on a breaking fast meal (breakfast usually).
Jennie still gets a tablespoon of Farmer's Market brand organic pumpkin if I think she needs a little extra help.
The Vet's Best is primarily psyllium (50%) which can create too much bulk in the stool if given too much of or too often, I suppose that's my only con against it. The SEB and marshmallow are ok at 25% each.