In my opinion, I think the Black Cat Models versions are better - the printing is cleaner with less striations, which is a by-product of the printing process. The printer used by BCM is newer tech and it shows in the finished product. Also I think the detail is bit better. Assembly is about the same.
The price for 4 guns from BCM is about $9.60, which includes VAT. If you are a non EU resident the VAT is discounted so the price is less but I don't know how much less. The 3D Model Parts offering is also 4 guns (though my review sample had 5) for $7.49. So even if the BCM versions are a little more cost wise, they are the better of the two in my opinion.
I hope this helps,