Many Set-top Boxes are produced for the broadcaster where its only possible to use their card .A good example a this are Sky Boxes. Generic Set-top Boxes refer to digi boxes that are manufactured to access all Free To Air (FTA) satellite and terrestrial TV channels and not limited to one braodcaster.
Some generic set-top boxes are sold as satellite only or terrestrial only or sold as combos where they can access both satellite and terrestrial signals. Many makes of generic set-top boxes also have the facility to insert subscription cards.
Here in Valencia there are numerous makes sold . If you go to the Demon Multimedia website (you can change the language to English with Google Translate) you will see the wide range available and their prices. I would avoid buying the kits and set-boxes from Lidl or Aldi . They claim to access hundreds of Channels which is true for the German viewers who are accessing Asra 19° and Hotbird
I have installed many makes of set-top boxes. They are all very similar and often the internal parts are interchangeable between makes. What is different is the software with each company having their version of the software without a doubt the Illusion or Cristor box with the Illusion software is the best for the price. The menu and favorite lists are excellent and their tuners are very good. Both of these boxes are made by Tecatel in Gandia and they are same item internally with different cases
If you want to install your own system, It is wiser to buy a 1.2m or 1 m dish from a satellite shop and an Illusion Set-top Box. When you buy the box ask the Shop to install Illusion Software on either the Illusion or Cristor Box. The box is often sold with KYNG software which doesn't have a good system of favorite lists. If you go to this page you will get detailed instructions for the Illusion and Cristor Box
The only down side to the these boxes are that when you have a power cut the box may revert to the Spanish menu and lose the settings but wont lose the channels you have scanned. The second problem is that the external or internal power supply to the box is prone to fail with the power fluctuations of Spain. If the box fails to start take it back to the shop and they will replace it free of charge if under guarantee (2 years) or for a very small fee if its out of guarantee. The shop can update the software at the same time