Make sure you’ve done the updates! I’ve heard it can be slower on older mac’s but it works very well on my 2014 mac book pro. A 3+ year old mac also won’t be able to use some of the new features. The continuity features that let your iphone/ipad work as an extension of your computer are seamless with mine and being able to use your iphone as an internet hotspot is a good feature. For those that use a lot of social media and/or icloud the integration is better. For specific problems I'd look through the apple forums for, hopefully, good feedback.