ORAC,
Good catch and my bad. I should have said, 'one of the only two STOVL concepts to go into service and be operationally effective'.
My apologies.
Yak-38 could certainly do STOVLs, VLs, VTOs et al, but its operational payload was extremely limited as was its avionics suite. As far as I remember, it was withdrawn from service after only a few years. It also showed the issues a lift plus lift/cruise layout has to cope with, in particular the hot gases from a lift engine just aft of the intakes. The solution the Russians used was to extend the intakes a long way forward - works, but there is a serious weight penalty.
That's not to say that this concept can't work - but like all powered lift aircraft, the trade offs are complex and the concepts carry quite a lot of risk late into development and test. Sometimes into service.
Hope this helps and thanks for pointing out my omission,
Engines