Matan, thanks and glad to hear it!
Roman, I've got the H-variant that I've been building off-and-on for the last couple of months to the paint stage and didn't have any major issues with the Flakvierling. Other than the barrels which I agree can use upgrading to get the most out of them, I didn't see any other problems with the Flakvierling itself. You are right that at 4 barrels it can be a little pricey to upgrade depending on which barrels you choose. I selected the RB barrels from JB Model out of Austria and the price wasn't too bad.
http://www.jbmodel.eu/product_info.php/products_id/81 They currently show as being Temporarily Out of Stock but they usually restock on a frequent basis. Might give them a shot since you're in Norway.
Here's how they look fitted to the kit guns as an added reference.
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