So, dont even bother to get the MBAM paid version?
I have Windows XP SP-3 with just 512 Megs of Ram and it suits my needs just fine. Avast is my real-time protection. I just got Free Malware Bytes and like it, but prefer to just use it on-demand. Sometimes when you have two or more malware shield protectors running at the same time, memory and speed can become sacrificed. I used to have the other things like Spybot Search and Destroy and Windows Defender. However, they were slowing things down too much and found very little. Oh yea, I also had Ad Aware, which found nothing except tracking cookies for about three years!
My computer is old (over 5 years old) but it does what I need it to do. How much RAM do you have currently? How is your processing speed? You should probably have or upgrade to at least 1-2 GB's of Ram if you are going to have multiple real-time scanners. Windows Defender now comes with Windows Vista and I think Windows 7 as part of the OS. MS also has the upgrade for Defender called MS Security Essentials, which is MS's free Anti-Virus program. I heard it's OK, but Avast continues to surpass it in performance tests.
I just installed Malware Bytes recently. I think with that and Avast, you should be just fine. If you already have the free real-time protection from Avast, I don't think you need another real-time protective shield. Make sure you have the RAM to cover that if you want more real-time protection.. But I don't think you need the paid version of Malware Bytes as long as you have real-time protection from Avast.
Jack