The lower arm bar is as its name implies, ties the front lower arms for a more rigid assembly. So why is rigidity so important? Well anything that flexes too much including a car's chassis, bushes, tyres, etc. becomes a sort of a spring by itself except that unlike a car's suspension system this spring is uncontrollable which is not good for handling. Per Mike Kojima "The lower control arms front mount in our car (N16/B15) hangs out in space unsupported. This causes the lower control arms to move under hard cornering load causing steering inaccuracy and tire contact patch loss."
The room bar is the bar linking both the B pillars behind the front seats and also serves to improve the car's chassis rigidity.
All Ultra Racing bars are made from steel as opposed to lighter aluminium. Ultra Racing claim via its website that all brackets are 4mm to 5mm steel while hollow steel tubes and oval tubes are 1.2mm to 1.6mm thickness. Ultra Racing also claim that as steel is stronger than aluminium for the same size and thickness and that in order for aluminium allow to be as strong as steel it has to be at least double the thickness thus the weight saving is not so apparent anymore. You be the judge but I know which material I would prefer if I had the choice. Let's just say that the top Japanese manufacturers such as Okuyama Motor Sports aka Carbing offer their bars with aluminium alternative.
I have sent my Ultra Racing bars to be painted matt black and should get them back for installation in about a week. Stay tuned.