Are Yongnuo Speedlights good enough for my Nikon D3000?

I'm 15 and I've been into photography for 2 years already, but just a hobbyist. I have some savings (approximately 6, 000-7, 000 Php). Should I save more and invest on the SB speedlights of Nikon or getting Yongnuo speedlights are enough?

Added (1). Approximately 6, 000-7, 000 Php = $165

If you buy the Nikon SB units, you will have TTL (auto flash metering) when they are used on the camera hotshoe. The zoom head (SB600 & above) will also automatically adjust to the focal length lens attached (or as close as it can get it).It means that you don't have to think about setting the flash yourself - the disadvantage is, like with most things 'Auto' it can get the exposure wrong, and because it's setting it itself, you don;t know WHY it's wrong.

It's not difficult (and a lot more consistent) to use manual flash - and if you decide to go this route, then there's no need to speed £200 & up on a Nikon SB unit. The difference is that you set the flash output manually (in steps from full power down, eg 1/1 (full), 1/2, 1/4, 1/8, 1/16 etc). The Yongnuo range of speedlights are good value for money. I have the YN460-II (about £30) and the YN560 (about £40).

Flash used on camera is however harsh - it's flat frontal light. Consider getting a set of Yongnuo RF602 radio triggers (£18 - you can afford it with the money saved from buying a Nikon flash!). This will get the flash off camera which will allow more creativity, in terms of directionality of the light, and also allows the attachment of modifiers (umbrellas, softboxes, etc to soften the light).

A good resource for off camera flash is the Strobist blog;
http://strobist.blogspot.com/2006/03/lighting-101.html