Locks that work

Hi, picking up my cycle to work bike tomorrow.
In terms of locks is this cheaper one good enough:

Magnum on guard
Magnum ONGUARD Brute STD Bicycle Security Bike U-Lock LK8001: Amazon.co.uk: Sports & Outdoors

or should i just shell out for Abus Granit X-plus 54?

Anything else to consider?
Appreciate any advice, i'm a total novice!!!

Either lock is good. The very important thing is to make sure that there is a very tight fit, so no-gooders cannot get jacks and things into the empty spaces within the lock shackle.