Thanks Palal for the suggestion. Yes, I have an unlocked iphone that I can use as a hotspot for the other devices. As a comparison, the same companies are charging as follows:
- 25 EUR (5 EUR/day) with unlimited data for 5 days in Portugal and
- 40 EUR (4 EUR/day) with 2GB data per day for 10 days in Spain.
Total is cheaper then renting the pocket wifi devices from them. I still have to return the SIM cards, but it's less expensive to pay if the package is somehow lost.