All reasons to NOT use the SD855 S10s in Europe: VoLTE + VoWifi are certified for US carriers, RCS will prob not work, all LTE & 3G bands may not be present, and carrier aggregation is setup for US carriers. Phone might not use CA on non-US bands.
Data speeds are not guaranteed to equal the 9820 variant whilst on EU networks. Last but not least, warranty. This is valid within the US. Offers like free Spotify or iKonik are not promised for imports. Samsung Pay is available in certain markets, but you'll have to test it. Bootloader is locked and the US models are single SIM.
No problem. The availability of VoLTE & VoWifi are a matter of safety. With networks shifting to LTE + 5G you don't want to be stuck with a phone that can't even make calls.
If you ever find yourself in dire straits you'll be at the mercy of luck. Wifi calling at least gives an alternate means of calling emergency services, but this requires carrier approval (as well as VoLTE, Video Calling and RCS).
They addressed battery for Exynos with the March update (not day one patch). And read the Anandtech review, battery is quite similar. At 1st parity wasn't achieved, but Samsung has issued a few updates since release.
Alternately, wait for the Note 10, or S11 E9830. By then everything should better.
Unlike the S10, N10 has a chance of shipping with UFS3.0 storage like the Galaxy Fold. This will take read and write speeds further. RAM could be LPDDR5 (4X in S10). Battery size is a mystery too, tho it should be larger than what's in the S10+.
One other possibility is a ToF (time of flight) camera similar to the S10 5G. So there are good reasons to wait aside from software stability.
The potential for a refined product exists, especially given the availability of 5G modems (Qualcomm x50). Samsung also holds a patent for an S Pen camera. Whether the stylus will receive that upgrade in 2019 is anyone's guess.
But I'm definitely switching if that materializes.
