Strength of N1-CL1 Closeup Lens?
My guess is that the 3.8x is just a multiplicator of magnification of the underlying lens.
I.e. if the lens has 0.3x magnification, then with the closeup gadget it should have 1.14x. But I'm just guessing. Either way magnification of the lens has nothing to do with the crop factor.
I also think at 50 eur it's rather pricey. For a price not much higher, one can get a 1) an adapter from N1 to any mount 2) a reverse ring for said mount, 3) a 50/1.8 lens for said mount. Some great macro right there and a 50/1.8 lens for telephoto use to boot.