general reliability of a brand, that sells like dozens of different types of products? come on, you can't say that all smsl's have hiss, popping and reliability issues, simply based on what you've read about on single model (which wasn't good, btw).
personally, i don't have the x4. however, i know a very reliable local guy, who bought it and reviewed it. he wrote about it multiple times on hungarian boards, and based on his experience, i would definitely put it on my shopping list if i were to buy a cheap portable dac/amp. he wrote that the dac has a typical musical wolfson sound, works with all systems like a charm, has a quality build, and can recommend it to ear-/headphones that are relatively easy to drive. i trust his judgement 100%. i would definitely pick the x4 over the hifime sabre dac, as the latter might have some issues with android 6/7 systems. also, i do think that the x4 looks badass in red, but that's just me.