If you are considering a Finnex light I'd encourage you to look at the schuber wright tank combos on [Ebay Link Removed] aquavibrant has them listed cheaper there.
I have a 4g low iron schuber wright tank and I love it. I keep saying I'll get another (bigger) but I haven't found the space in my house for it yet It's either going to be the 9gal SW or the 17.4g Mr Aqua - I just have to decide, and figure out where to put it.
Finnex LED is very very bright and suitable for that tank size. I would say it is better than the Arhaea 27W fluorescent light.
Glass cover is not necessary unless you want to keep your fish from jumping.
I disagree. I had better results with the Archea (I tried both lights) on my Mini M. With the Ray I it just wasn't enough light. The Ray II had some improvement (the HC grew slowly and it wasn't compact compared to the growth I had with the Archea) but still wasn't satisfactory.