He makes a really good point that the deadline of a writing competition can be both a blessing and a curse. While it might incentivize a new writer to finally finish the script that might otherwise languish incomplete for years, it is also in danger of encouraging them to send off a script before it is ready. You only get one chance to impress so make it count. Make sure your script is REALLY ready.
My advice is to see writing competitions as just a part of your overall strategy to further your writing career. Some competitions may be better suited to you than others. Moviebytes have a great system of rating US competitions and while we don’t have anything quite like that in the UK, you can ask around (Twitter, Facebook, etc) and find out what experiences others have had who may have submitted to the competition in previous years.
The other great way to judge a competition is by its judges. This element, far more than any cash prize, is where the real value lies in submitting to some writing competitions. You may be desperate to get your script into the hands of a particular executive at a particular production company or studio because you are sure your script is right up their street BUT they don’t take unsolicited submissions BUT said executive is on the judging panel of an open writing competition. If your script is good enough, it will end up being read by them and you’ve brought yourself to the attention of someone who might genuinely be able to progress your career.
As with every other element of breaking into screenwriting (approaching production companies, getting an agent) make sure you DO YOUR HOMEWORK! The rest is down to the brilliance of your writing and your determination.