If it looks good - that is more of a personal preference than anything else. Generally speaking - darker colored cars would tend to make these type of tail lights "pop" out more. But if you only added these lights and had no other modifications to the vehicle - would make your ride seem a bit unfinished or look weird.
Also keep in mind that, even though these are DOT approved - you might get still get hassled by the local law enforcement - not worth it for a small change in look.
Some OEM cars are coming with "altezza" like lights - but be wary of aftermarket "altezza" - unless they are made by a reputable company, I've seen many leak, have the foil lining peel off inside or get wrinkled, or not fit correctly to your vehicle.
If you are determined to get them - to remove your tail lamps - peel back the trunk liner - locate the screws and/or clips that hold on the lamp assembly - disconnect the wiring harnesses and carefully remove the lamp.
IMHO - going for the flash or "bling" is OK - your car is an extension of your personality and people are free to make whatever modifications they want to their own vehicle as long as those modifications fall inside of rules and regulations set by local / state / federal transportation safety laws. But you find that most people will quickly tire of the look and will trade the "show" for more "go". That is probably why this is on EBay to begin with.
Good luck