From a very quick glance, it seems that Interslavic is to Slovio what Interlingua is to Esperanto.

Esperanto is a language that's simple and easy to learn (at least if you're familiar with romance languages), but not necessarily easy to understand if you're not familiar with it.

On the other hand, if you're familiar with 2 or 3 romance languages, try to read https://ia.wikipedia.org/wiki/Interlingua. Even if you've never heard of Interlingua, you'll probably understand most of it. Interlingua is optimized for easy understanding, which means that it adopts common words from romance languages even if they're not totally consistent with the rest of the language. This means that ease of understanding comes at the cost of language consistency and ease of learning. For people in central Europe, I'd say Esperanto is easier to learn (to speak) and Interlingua is easier to understand.