OK, here’s a few simple facts. I’ve got experience of those Apollos from working on them in the shop.
1- The brakes are, quite frankly, dangerous. It would be safer if it had V-brakes as the ones supplied do not work- the pads fail to grip the disc properly and the lever pulls to the bar when the brake is set up so it doesn’t rub. Also, once the pads wear out they can’t be replaced as spares aren’t available.
2- The forks don’t work. They will seize up within a few months. They’re also plagued by play- they rock back and forth due to poor tolerances and bad manufacturing.
3- The wheels are not up to proper mountain biking. They’ll handle a bit, but the hubs are very basic and the bearings will collapse very quickly once dirt gets inside.
4- The drive train, while simple, is reliable which is good. However the left hand crank arm is made of very soft alloy and it’s fairly likely (though not certain) that it will come loose and need replacing.
The Carrera Subway, by comparison is a better bike.
1- The brakes, while not the best, are of a reasonable quality being Shimano and are reliable. They work better than a V-brake and you can get spares.
2- The fork is rigid, but because of this it’s lighter and more reliable than the poor quality suspension fork fitted to the Apollo. It will do its job and stay safe. Rigid forks will also teach you skills and make you a better rider when you have the funds for a more serious bike.
3- The wheels have mountain bike rims. Again, the hubs aren’t the best but they do have some basic sealing and we’ve never seen any problems with these wheelsets.
4- The drivetrain is a step up in quality. The cranks will handle off road pretty well and the gears will keep behaving. Also the cassette is a proper cassette, not a freewheel (where the cogs and freewheel mechanism are a single unit) and so much more reliable.
So, while the Carrera appears more basic, it’s a higher quality product and will last you a lot longer. The tyres are cheap and easy to replace and then you’l have a decent enough bike for learning XC on.