@Grumpy Gnome Indeed I think that for things that need to be reassembled often other materials are better, like the core space cardboard terrain you mentioned (despite not being perfect). Still the connectors and modularity can be used as an advantage, since you can have several individual buildings/sections with their individual parts glued together and then use the connectors to simply keep the different sections together on the table so you can have different layouts with fixed sections.
I have built mine as a collection of individual buildings, but as you can see from the previous picture they go well together either as independent buildings or as part of a larger fortification.
If anyone is interested in the full layout, this is what I have built from a single military compound box (I stilll have some spare parts):
https://i.imgur.com/hUBAtO5.jpg
https://i.imgur.com/nZNOHg0.jpg
https://i.imgur.com/cgJjMIZ.jpg
https://i.imgur.com/nKj4g4U.jpg
https://i.imgur.com/Tm9Kidw.jpg
https://i.imgur.com/TK5H6e0.jpg
https://i.imgur.com/w7xUqoq.jpg
https://i.imgur.com/9BIqCR7.jpg
https://i.imgur.com/PYiTA00.jpg
https://i.imgur.com/9H385c0.jpg
https://i.imgur.com/4Ujzy97.jpg
https://i.imgur.com/V70S556.jpg
https://i.imgur.com/uTfwDkm.jpg
https://i.imgur.com/t2v9lc6.jpg
https://i.imgur.com/iOlC2zr.jpg
https://i.imgur.com/ZflX6Jb.jpg
https://i.imgur.com/Jq5IQYZ.jpg
Intentionally as links to avoid saturating the thread.
Close up's on the first building I have done with those parts:
https://i.imgur.com/VaDIiRc.jpg
https://i.imgur.com/f71WkHG.jpg
https://i.imgur.com/uO3llNs.jpg
https://i.imgur.com/FQBSBHm.jpg
https://i.imgur.com/AjFm05o.jpg
As you can see a single box can be used to make a large amount of terrain and there are some beautiful parts within the set. The minis should provide a good sense of scale despite my lack of skill as a photographer. I have glued the parts of the individual buildings as I didn't want to rely on the connectors to hold without glue, nor spend a while filling down some of the holes to make the connectors fit more easily. The fact that the holes for the connectors and sometimes the connectors themselves are visible can be a problem for some, but in most cases they can be easily disguised, by putting them on the inside (not always possible depending on what you are building due to space constraints when using all the connectors in one side), as the connectors fill the holes and leave only a slight depression on the opposite side that you can easily cover with greenstuff or with some decorations. For covering connectors on the outside it can get trickier as you would need larger decorations to cover everything, but it is still feasible.
I think the issues that Mantic's design has are mostly the issues that you see with modular designs, as in the attempt to provide versatility, you end up losing some things in the process. Like always it is a trade between versatility and the ability to go together seamlessly.
Once I get some more space for my terrain, I am thinking about getting 1 or 2 additional military compound boxes, to either build a larger fortification or several small fortified buildings.