More info required.. Got url link to manufacturer website and detailed product description and specs? If you can't easily find such? I suggest you ignore the recommendation.
Perhaps bad cable.. Why no use HDMI? Less to no hassle.. RCA cable (carries AV signals) connects to AV port(s).. SPDIF/TOSLINK carries digital audio only and connects to its compatible port.

As per your initial question.. "If this is a good and reliable brand". IMO, No it is not. It seems to me like a less popular EVPAD option and I don't even like the evpads  .. Basically, they are an ehem iptv provider that bundles their app with a box that's branded as theirs. Found the specs page and have to say, hardware wise (and if primarily for iptv purposes), it's actually not bad. Which leave firmware performance.. Which to me is unknown. Hence my recommendations to ignore. Unless you've tested the hardware yourself and it's okay, or its so good and can only be accessed via their branded box..?.. Else, I suggest you stick with the generally accepted opinion here. Ask the seller, say you bought another box yourself, can the svicloud app and service be used on it?