I've used a machine with this chip (remotely). It's not terrible; Daniel Lemire blogs about some early performance impressions here https://lemire.me/blog/2019/03/26/hasty-comparison-skylark-a... and I've ported simdjson to it (https://github.com/lemire/simdjson).

I'm definitely not at the stage where I can say anything definitive about performance. For a SIMD-intensive task, a preliminary run on a 3.3Ghz eMag core gets about 400 megabytes/second of JSON parsing relative to 2.2 gigabytes/second on a 4.0Ghz Skylake. This may come down to having a maximum of 2 x 128-bit NEON operations per cycle vs 3 x 256 AVX2 operations per cycle, as well as some clock speed differences. Will eventually post about this at branchfree.org when I don my Nomex long johns (required whenever doing any benchmark that might imply to anyone that any processor runs faster or slower than any other processor).