why did they say not to get it?
when you're starting out cat5, you don't need a bling bike. in fact i'd be afraid of riding a nice bike for cat5 due to the noobs and crashes.
just get whatever you think you'll enjoy riding the most so that you ride more and become faster. it doesn't really matter what you ride, i'm sure there's a huge range of bikes in cat5. then when you're really into it, you'll have a better idea of what's best for you and might go for a better bike.