The Rubik's DIY is definitely a viable speedcube. It turns amazingly fast even when not lubed since it uses a high quality, hard plastic. (The cube I have that most closely compares to the Rubik's DIY is the GhostHand Ice/GhostHand Blue Magic, if you've felt one.) Unfortunately, the classic design is in no sense sophisticated, so you will still experience lock-ups on tight tensions and pops (or explosions) on loose tensions. Nonetheless, it is possible to achieve fantastic times using this cube if you take the time to get used to it.
That being said, I would recommend a bunch of other cubes (which are cheaper than $10) before recommending this one. For instance: FII, AII, AIII-f, even the YJ and DianSheng. (The DianSheng is similar in feel to the Rubik's DIY, if a bit slower, but it's less than half the price) And of course, as someone else mentioned, the amazing ShengShou Aurora!
Hope this helps!