Bad idea to buy laptop without authentic windows? Is RemoveWAT good? I need advice!?

My friend is selling a nice powerful asus laptop wihch I really like. The big problem with it is the fact he apparently wiped it clean at one point, and that included windows.

He installed this windows 7 that is on a miscellaneous plain written on disk and got me the drivers for the wireless. I asked him what happens after the three months goes by and he told me just a disclaimer appears in the bottom right corner. I looked it up, though, and it appears that you also have to deal with a black background and only the most important windows updates. I have borrowed the laptop for a few days and now I am trying to solve these issues.

I need to know my options. I already tried a keyfinder but it found a key that didn't work.

I just put on RemoveWAT even though I won't have to deal with the disclaimer for three months, but I am not 100% on how it works.

- Does RemoveWAT just hide the disclaimer and activation notice? Do the other effects, like black background and no good updates still happen? Is RemoveWAT a good option? Are its effects permanent?

- Is KMS activation a viable option, and is it better than RemoveWAT?

- Is there some way I can uninstall this unlicensed WIndows and then restore the original Windows that was lost in the wipe, and use the activation code on the bottom of my laptop and not have to worry about all this?

- Is this laptop worth buying at all? It is an excellent price for the power, but lack of original Windows makes me nervous