What are the problems associated with renting a “European” or “Worldwide” pocket WiFi?

Cost and Performance
All other rental hotspot options that allow you access the Internet in multiple countries are based upon roaming, and for this reason, they have the same problems.

Usually they use the UMTS standard, which is the least performing of the 3G, and have a daily limit of a few Mb per day (best case scenario the device has the limit of 100-500 Mb per day).
Over this daily limit the speed is drastically reduced making the hotspot practically unusable.

And, to conclude, all of this is typically offered at fees double or triple to the ones in respect to WiTourist!