Yes they are very like Advances, except that you can plan in breaks of journey and vary your route much more easily.
Once you have booked the journey the way you want it, you must travel on the ES, IC/EC and ICE trains specified on your ticket and itinerary. However, if your trip includes Regional trains (it will show as NV on your ticket, and RE, RB or S on your itinerary), you can use any train for that part.
If your ES is delayed, follow the advice on
www.seat61.com WRT Brussels. This is because you won't want to wait 4 hours for the next ICE, but catch a Thalys.
If your train within Germany is delayed, you should get the conductor to endorse your ticket, but if not, speak to the crew of the next train before boarding; you are very unlikely to have hassle. If you are late into Brussels from Germany, just go to the ES checkin. Again you are unlikely to have problems.
Also, in the worst case, DB operate generous delay repay, which comes as an e-voucher which you can use a bit at a time (if you want).