This is my favorite LN series, so take it as a biased opinion, but these are the only LNs I have physical copies of. They are actual hardback books unlike most other LNs I have looked at in the past (Overlord is the only other one I have thought about buying in the past that is a hardcover). My only complaint is that the official English translation is super slow. The Japanese releases are two volumes ahead right now with no announced English release of LN5 yet.
Glad to see another TEIS LN fan. The downside of being the only LNs I own physical copies of is that they don't really fit in with the other books on my bookshelf.