I've not tried the HT 4018 yet but I'm considering adding it to my hams' diet to supplement the seed mix. I've talked to a few people who are using it and there are a some pros and cons, as with all food options. The biggest pro is that it is a primarily wheat-based block as opposed to corn or soy, and that there are no molasses in the ingredients. The con is that it is low in fiber (3.5%) and is not as compressed as other brands, so it's not a good substitute as chews. The low fiber is my initial concern, but I was advised that if you are also feeding a good seed mix and fresh veggies daily, then it is easy to make up the fiber requirement.
A 40 lb bag is huge!
If you want to try it out in smaller portions, try
thecraftyrat.com for sampler or 2 lb bags. They're on vacation until March 5th, so I won't be able to make an order until them.