I use my IP as a slow cooker all the time and have never noticed a difference or problem.
Do you currently own a decent crock pot (apart from the one you mentioned that was no good)? If so I'd start with that. BUT if you need to purchase something I'd 100% absolutely with no hesitation purchase an IP. Start price watching and get a good deal but TOTALLY worth it. I am a die hard cook and spend LOTS of time in the kitchen (I LOVE to cook) and most definitely my IP is my most used appliance.