Note that there are just a very few such HTLs-mostly AO and Meininger. Both are (german) chains with combined HTL and hoStel (=multibed) and most have guest-kitchens. They also have a few in AT/CH/HU/CZ/FR. Meininger in fact has a very good modern HTL-room standard. AO mostly does big and very noisy (saufen) german young schoolgroups-when these are allowed again to travel. Nearly all are very conveniently located close to stations.
They mostly give 10% discount, by quoting like Eurail or Interrail on the booking. Same often for hoStels on sites like hostelworld.com
Note that about each and any city in which they are also have dozens/hundreds of other HTLs that maybe do not give discount but are still cheaper in final price. USAers tend to stare blind on that magic word ´discount´ but it means nothing. Use as 1st step general comparison sites like booking, then try to find the site of the place you like and book direct for better prices (less commissions). The USA seems to favour pricewise/line-but thats nonsense for EUR.