P&B is just psyllium and liquid Bentonite shakes...Holistic Horizons uses no Bentonite and is a 2-part fiber and herb program and involves drinking shakes of one of their Bulking Agents (psyllium and a few herbs) and taking an Intestinal Cleansing Tablets that includes herbs to soften and loosen mucoid plaque, and also blood and lymph cleansers. Some of the herbs in Holistic Horizons program also assist in cleansing and supporting the liver and help to address candida and parasites. You can learn more about HH from their website...run a search.
P&B is cheaper and generally produces mucoid plaque more quickly... for some it is as little as a few days. But some people also have difficulty using p&b as it constipates them. For people who are unable to use p&b, some of them find that HH does not back them up in the same way. HH is more expensive and generally works more slowly...but has some added benefits of blood, lymph and some liver, candida and parasite cleansing.
As for taste...p&b is pretty non-descript...very bland and a bit dusty tasting...or maybe sort of cardboardy. (LOL...no, I don't eat dust and cardboard...but they smell a bit like the shakes taste!) HH shakes vary depending on which Bulking Agent you use...the Special Bulking Agent has a fairly strong clove taste....I understand Bulking Agent III also has cloves...and I believe Bulking Agent I has an oniony sort of taste. If the flavor is objectionable with any of these you can mix them with fruit or vegetable juice...you just have to make sure that you drink additional water too. I think more people have problems with the texture rather than the taste of the shakes...psyllium can gel up very rapidly. I have found that making the shakes in a lidded jar or cocktail shaker, using cool water, and drinking them as fast as possible helps in getting them down easier...while they're still thin.