I use all the following in combination and found that just having one wasn't enough to get the detail I needed. If I'm looking something up I get out the whole group of books. Individually there just isn't the complete breadth of information to find what I'm looking for usually:
I would recommend the Langhamer book for historical information and detail on the engravers/decorators (the most famous ones) and manufacturers. The first 86 pages are good for me but really there is only a small section in that 86 pages I'm interested in.
It covers the information I find when I'm looking up academic publications which have been published in German or Czech and looking for information on history of factories/makers. So actually I could probably do with just re-reading it from cover to cover again.
The next 230 pages are not an era I collect, but it gives an excellent and detailed overview of the glass and designs for the periods and some incredibly fantastic photography. I love looking online but for me, for some reason, seeing a picture in print seems to enable so much more detail to be seen.
I have the Das Bohmische Glas set of volumes, plus some Walter Spiegl, and the Farbenglas 1 and 11 Walthraud Neurwirth, and some more maker specific books for the period 1850 and earlier etc but they're all in German. I use them constantly though and love looking through them. But I find it quite hard work translating the information in detail.
And of course the Neuwelt to the Whole World book which is also in English. Again, I stick to the front of the book mostly. But it's great and I use it constantly.
The Das Bohmische Glas books band 2 is the one I use most. Band 3 just for checking I've not got the date/timeline wrong on something. They are in German though. However they cover the other makers and not just Harrach so they are fantastic for that.
The Farbenglas books are amazing. They have photographs but they are smaller books and really not about the pictures to be honest. They are of glass that was deposited in the Technisches Museum Vienna at the time the glass was made, so it's very detailed and very specific. They are incredible. The detail and information on the colours, how they were made, when they were made, the glass that was exhibited in the Exhibitions of the Biedermeier period, just fantastic information.
If I had to recommend, I'd say get the Farbenglas 1 and II
And the Harrach book.
Then it's good to get the Das Bohmische Glas Band II as it covers the other makers in more detail and gives good photographic examples.
But then you need the Langhamer book for the detail and information as well.
This is the group I use most