What are the differences between ZAX's "Secure Online Backup" feature (which uses IDrive for this service) and IDrive's "Basic" plan?

The "IDrive Basic" plan is free and offers 2GB of storage, while the "Pro" version offers 150GB for 4.95/month.
ZAX appears to offer the exact same deals, so I'm unclear what differences (if any) there are between the two approaches.
Thanks,
Larry

Operating System:Windows XP Pro
Software Version:8.0
Product Name:ZoneAlarm Extreme Security