Yep, that's why I call that a tradeoff. Far from perfect and yet so much better than nothing.

Pros:

• Likely cuts 99.99% of attacks.
• Nothing to do on client's end.

Cons:

• Whitelisting must be updated everytime the client address changes.
• Not 100% bulletproof as operators (notably for mobile networks) can NAT multiple connections behind a single publicly addressable IPv4 address.
• Also IP addresses can be spoofed but I doubt that would be a major concern here.