Aged gouda is my favorite cheese!
Beemster Classic Aged is like a firmer, creamy, sweet, slightly sharp, nutty version of regular gouda.
I've never had a 5 year, but 2 year aged gouda (like Beemster xo) is kind of like a creamy parmigiano but not as hard... nutty, caramel/toffee flavors with random crunchy tyrosine bits.
I would expect the 5 year to be comparable in flavor to Parmigiano with more creaminess and a less crumbly texture due to the fact that gouda is made with whole milk while Parmigiano is made with partially skimmed milk.
Truthfully, it rarely lasts long enough for me to use it in anything... it is the perfect cheese to eat by itself or with apple, pear, or almonds. You can basically use them anywhere you would use a sharp cheddar or parmigiano.
Just as important as the bacterial culture is the use of rennet in cream cheese, which aids in the removal of liquid whey. When making cream cheese, the point is to drain much of the whey, resulting in a semi-solid texture. Rennet helps encourage the solids to curdle and squeeze out liquid. Yogurt doesn't necessarily include the draining step, though it can be done if you're looking for a thicker Greek-style yogurt. In this case, the acid produced during fermentation while making yogurt aids curdling and helps produce the final texture.
In fact, it's possible to take the draining process even further with yogurt, resulting in what's often called yogurt cheese or labneh. The final texture can vary a bit depending on how long it's drained, and whether you use weights to encourage the process.
In my experience labneh still never gets quite as solid as cream cheese, but it's pretty close when sufficiently weighted and drained. Labneh also retains yogurt's tangy flavor, which is mostly an effect of the bacterial culture. Though I haven't measured, I would expect that the pH of labneh is lower, so it's probably not always appropriate as a direct substitution for sensitive applications like baking. In other places, you could definitely use labneh instead of cream cheese. If you're having difficulty locating cream cheese cultures, this would be the easiest tack to take.
I haven't tried (or seen) both rennet and yogurt culture used together, but my suspicion is that it would take the curdling action a bit too far for the result to be smooth and spreadable.
So, tl;dr: the major difference is that yogurt culture is calibrated to produce a higher level of acid, resulting in a tangier flavor and reducing the need for rennet to curdle the solids. If you follow the same procedure, varying only the culture used, you'll have a reasonably similar end result.
Best Answer
It is calcium lactate crystals. It is safe to eat. On regular cheeses it is a sign that it is aged well. For packaged, sliced american cheese I am not sure I would care for it. But it is a matter of personal preference.