Kringlan is easy enough to use when details line up, but the fragile parts are exactly the parts travelers care about.
Check Kringlan's official site for current shops, restaurants, services, opening, cinema, play-area, and mall information. Check Reykjavík City Library if the library branch is part of your plan. Check Strætó for current stops, route numbers, fares, payment, and service notices before using Kringlan as a public-transport anchor.
Driving and parking details should also be checked close to the visit, especially during holidays, events, construction, heavy weather, or peak shopping periods. The best Kringlan plan is practical and flexible: solve the errand, eat if it helps, then move back to the Reykjavík stops that carry the real visitor value.