I don't think you know why you want to get this lens yet. Don't let the BBB control you (*not before you understand why you need it*)
Any lens is good for portrait taking (as in all lens can take portraits). It depends on how you utilize the lens in the given environment. (you can even take portraits with 55-250

, depends on how you frame it)
One can use the kit lens 18-55 and still shoot marvelous portraits with it.
oh, btw, 18-55 + 55-250 is quite a solid combo itself enough to cover "general" photography from wide to portraits to tele.
*don't be too fast to discard the 18-55 if you own one, despite what many may say(e.g. abt the IQ, non USM), I still think it's a great lens*