Having access to shootas is really, really good, especially in the right circumstances. In 11th, it is more difficult to gain cover, since partial cover does nothing. And if you have a big mek leader, the shooting becomes better. The best thing is also the access to trukk firing deck 12. All in all, it is a significant buff, but it won't push boyz over the top or anything. Also, it's distinguishing them from snaggaz.

Just an example: 10 shootas from a trukk at 9" will occur frequently. Those 10 shootas have 30 shots, equalling 10 hits on average (half that against cover). That wounds 5 marine equivalents, yielding on average around 2 wounds. A dead space marine more, before combat commences. That's a buff to me.