Selenium is best taken just after you use something that sinks the growth of biofilms in the digestive tract. If you have been doing an intestinal cleanse like diatomaceous earth, drinking borax water, supplementing zinc, butyrate or essential oils, that is an ideal time to have your selenium.
You will do just fine with the selenoExcell product if your body is sufficient in methyl-group nutrients (like thiamine, methionine, cysteine, TMG or Sam-E).
Supplementing any nutrient will up the body's need for it's cofactors, so if you get side effects like motion sickness, diziness, etc, research what foods you need to eat to ease up the selenium load (by upping it's co-factors), and for a short time discontinue the selenium.
The ability to digest the dead bacteria in the selenoexcell will depend entirely upon how well you digest the pill. Having it with a bit of straight (undiluted) fresh-pressed lemon juice and olive oil is a good way to trigger the body to digest it.
I cannot say left or right on Clark's thoughts on sodium selenite. It's likely the body uses and stores it in several forms, sodium selenite being one of them. A key would be to learn which tissues are richest in sodium selenite in a dissection of various mammals.