Are centrifugal turbojets easier to make than axial ones?
Centrifugal is easier to make.  It's just a big vacuum cleaner with a kerosene burning furnace behind it instead of an electric motor.  You have a one piece impeller, as opposed to numerous little blades and discs, and can be cast or machined from a block of metal.  It's not dependant on the aerodynamic lift of blades to force air from a large space into a small space. It just pulls it in and flings the air out into a small space, so it's more resistant to surge.  To get surge in a centrifugal compressor engine you have to really obstruct the inlet, whereas with an axial engine you just have to disrupt the flow enough to induce blade stall.

So in the 30s it was WAY easier, cheaper, and faster, development wise, to get a nice running engine using Whittle's design with the centrifugal compressor.  The big downside is that it is less efficient than axial. You can't get the compression ratio that you would get  with an axial because it's difficult to incorporate multiple stages, and the engine is quite large because of the need to fling air out to compress it.  The Germans went with legions of expense, grief and operational delicacy for the better efficiency and smaller profile of axial.

The most obvious example today is the fact that nobody uses axial compressors for turbochargers and most in fact use similar impellers as the turbine as well.  You won't see axial compressors on any of the little micro turbojets used in RC.  A lot of smaller turboprops also use centrifugal compressors, sometimes in combination with axial stages. 
That should tell you something about how much easier and cheaper it is to make.