Never done hopper flight, but too long of a train ride this time so going to try it. Reasonable priced, but no experience with it. Do we book those flights before leaving US? Or try and do them from Brussels and Prague? Would like to do here for just ease of laptop, language and time. But thought I would put it out there for any suggestions on past users of Skyscanner? And for any other helpful hints with these short flights.
If you know what flights you're wanting, book them now. I don't think you'll benefit from trying to book them on the spot or the day before. I can't tell if you're indicating that you're wanting to book on the Skyscanner site or some other site....don't book with them - it's better to buy right from the carrier.
Once upon a time, when budget airlines like Ryanair and Easyjet were new, they often had last minute sale fares as a promotion. Those days are long gone. Now, the longer you wait to book a flight within Europe (on any carrier), the higher the price, and the less expensive flights and/or the most popular times often sell out. So, book as soon as you know your plans.
Skyscanner will often give you a choice of websites to make the actual booking (they don't do bookings themselves). You should use the website of the airline itself, so you can see all the conditions, rules, and requirements. Many of the complaints about using low budget airlines are from people who didn't read the rules, didn't understand the rules, or didn't think the rules would be applied to them.
If your bags are over the carry-on limit (and if you're using a budget airline, they most likely will be), be sure to pay for a checked bag at the time of booking. It's much more expensive if you wait until you're at the airport. This is another reason to do a dummy booking for each airline option (up to the point where you put in your credit card). The "legacy" carriers like Polish Air can be cheaper in the end, as they have fewer extra charges and more things are included in the base ticket price.
Be sure you know which airport your flight is using. There is Brussels Airport (BRU) and Brussels Charleoi (CRL), which is much farther from Brussels itself. And some budget flights to "Krakow" are actually to Katowice (KTW), which is about 1.5 hours from Krakow (Krakow's own airport is KRK). As long as you're prepared, this can work. But do factor in the extra time and money if you're using the more distant airports.