I'm just concerned that running the two will bog down my system as SD did.
I only have a lappy with a PIII 1.2 & 512 Ram. And dial up as well.
with such a configuration it is indeed reasonable to stick to a
one security software configuration...you don't have much RAM and your CPU is slow. Even Avast alone on it is kinda mad. Someone in my family is running an old laptop with exactly the same configuration (P3 1.2 & 512 MB ram), Avast on it is unthinkable, but AVG is OK.
And second, running several resident AV as you know is not advised. MalwareByte is not an AV I know but sometimes, or often (?), the border between spyware/malware and viruses is really blurred, and even MalwareByte could conflict with Avast it the case both would attempt to access an infected file and take care of it, resulting in none of them being able to block it...this can just happen. This said it's no problem having MalwareByte free on board and do manual scans with it off and on. From what I hear it's good at detecting stuff others don't. Only thing I'm sure about is MBAM like SAS scan your registry, which Avast doesn't unfortunately. So again, go for it, but avoid any multi-resident solutions