The difference between Crisco and hi-ratio is in the amount of emulsifiers, and stabilizers, etc. Hi-ratio has MORE emulsifiers, etc. than Crisco so it can ABSORB more liquid without breaking down:
The difference in the two types of shortening isn't flavor/taste improvement (I don't find that Crisco or Sweetex have a discernible taste) but in improved performance and the absence of the "greasy" mouth feel that is an often heard complaint directed at regular shortening based American buttercreams.*
When I initially switched from Crisco to Sweetex, I tried subbing at 1:1 ratio. While the resulting recipe was not "greasy" at all, the general consensus was that the frosting was too rich (had too much fat) and was like trying to chug heavy cream (when you were expecting whole milk).
I then switched to recipes that specifically called for hi-ratio and have been quite pleased with the results. I find that hi-ratio recipes use less shortening (and make a better frosting) so that the higher cost of the hi-ratio is offset somewhat, making it more budget friendly.
CakemanOh recommends using 1 cup hi-ratio to 7 cups of powdered sugar, or substituting 2/3 cup hi-ratio for 1 cup of Crisco.
When trying any new recipe, I usually make only 1/2 or 1/3 as a test batch. Might want to try doing this when substituting hi-ratio for Crisco and see what replacement ratio you prefer.
For hi-ratio recipes, please visit this thread:
*Of course, not all Crisco based frostings are created equal.
Examples of some highly rated (non-greasy) Crisco American b/c recipes: