Technically, yes. Cost-wise, the Murena offer might save you lots of added taxes, import charges, customs etc. though. If you want to do a proper cost-comparison, ask the folks over at Fairphone owners in the USA (FP2 FP3 FP4).
Last but not least, the Murena offer must give you the same Support that Fairphone only gives you in Europe – this does not really apply to self-imported phones, or is much more complicated. Again, ask the other US FP4 users for details.