I was able to see the Cube. It looks like a good entry level bike. I think trails would be preferable to London streets, from what I hear. Are the trails close enough that you and the wife can ride regularly? I love trails, but I live in the desert SW and trails are everywhere.

The components are always a big consideration as is weight on a new bike. But the bike should give you a couple years of fun. Keep it serviced and adjusted and I think you will have a great chance to see how you like mountain biking. I ride both skinny and fat tires. I prefer the fat tires as it give me more of a full body workout and the terrain changes as does the scenery. I get more of a full body workout. How you both enjoy it.