I'm a BIG fan of the HT rodent lab blocks--they've been the staple food for my pet rats for a couple of years now. When I decided to get a hamster again, I did quite a bit of research (I'm a bit obsessive when it comes to the diets I provide for my pets haha), and ended up finding quite a bit of conflicting information as well as recommendations and statements that I really couldn't agree with based on the knowledge I've already gathered over the years about small animal nutrition, different brands of food, quality of ingredients, etc. In the end I chose to feed HT 2018 as the staple/base of the diet and supplement with organic grain and seed mixes that could be scattered around the substrate to encourage foraging along with appropriate fresh foods. While I do like that there are a variety of formulas to choose from (2014, 2016, 2018, etc.) personally I felt that both the nutritional values and ingredients of the 2018 were most appropriate for my Syrian and just like Biscotti mentioned how fiber levels can be increased via supplementation, the total protein and fat levels in the diet can be either increased or decreased depending on foods used to supplement the blocks.
And Biscotti--wanted to tell you that I've actually tasted the HT blocks myself too lol. Every rat I've owned or fostered has LOVED them and my dogs seem to think they're extremely desirable treats, when I had one of the rat cages in the hallway for a while they would all crowd around whenever it was feeding time in the hopes that I'd drop a block or two or some might possibly fall through the bars, and I have to be very careful to keep the bag well out of the way where they can't access it or else I find them all crowded around gorging as quick as possible before being discovered. I've always thought they smelled pretty pleasant, especially when compared to other brands of lab blocks/food and curiosity got the best of me one day and I decided to taste one. While definitely not something I would *choose* to eat lol, to me it really just tasted like some bland, super-healthy, multi/whole-grain cereal basically. But yeah, won't be pouring milk over a bowl of it for my breakfast any time soon