You get what you pay for. They will answer questions when it doesn't cost them money to send you a part. Most reviews seem positive, You will likely need your bike skills to set up the bike after it arrives with holes in the packing box. That's not Ecotric's fault. It's the shipping companies
Since they don't proudly say alloy, it's probably all steel, even the crank arms, bars, and stem. Probably cheap/heavy tires too. If you care about rolling weight and better acceleration, you can buy lighter tubes/tires. You'll probably need to upgrade to quality calipers some day, but at least it has disks. That is one trap of going cheap. If you know you want the goodies, you end up paying for them. We all know what a clunky bike feels like. It's probably near that spectrum, and maybe you can tune in the shifters/brakes to feel good, You will probably need to develop wheel trueing skills, but if high school mechanics in shops can do it, so can you.
The Dolphin battery is easily sourced as a third party part. If you ever blow up the electronics, a display and controller is around $100. A motor will be around $200-250. You know how to solder. I think the bike would be fine for a handy person who knows electrics and bikes. Not good if you want hand held service. With that view, any bike is good. LOL. That cannot be true.
As for 48V, I have what appears to be the same display in my parts bin. It's multi voltage compatible. You would have to look inside the controller to check the voltage ratings on the electrolytic capacitors. They come in either 50V or 63V working range. That will tell whether you can risk overvolting. My fatbike conversion was originally 36V and had a 36V only 500W controller. I upgraded to a 36/48V controller with 2x the power, and there's a 52V battery on it. Just for fun. I don't use the power.