Is there any advantages or disadvantages of either, i know single tip exhausts are way lighter, and I've see the hp gains of both and they are similar, sound of dual tips are a lot better on most vids I've seen. Is the flow better on dual tips or is there just an extra hole?

 

It's mostly a matter of esthetics, the dual-tip usually looks much more performance. On a ralliart it has no reason to be, since the air flow requirements of the engine are being met by practically any aftermarket exhaust.

Where a dual-tip exhaust is beneficial is if you have a V8 (or V10 or V12, anything with 2 headers) engine, with very efficient heads and approriate valve/cam setup and a fully double exhaust then it's beneficial.

But any 4 cylinder (inline) should be fine with a sufficiently large single exhaust.

A single 3 inches pipe flows 12% more than two 2 inches pipe. (EDIT: it's 12% more, not 18%)

 

a single will always flow better because of less turbulance/bends/etc

dual tips are purely for looks

V6/V8/etc can utilize dual exhausts, not dual tips, and benefit. but with a 4cyl, all the exhaust gases are going through one pipe. to split it at the end for dual-tips will disrupt flow

but performance difference depends on the car/setup. on the stock RA turbo, you're not flowing that much air anyway, you probably won't get a huge performance hit from dual if you really wanted the look