Oh man, using a different 4 lug pattern besides 4 x 140 is Subaru blasphemy! So naturally I never tried them.
Personally, I would find chevy six lug wheels and drill them to fit, they look good.
I have tried those, they were 15" on my 86gl with 2" lift...she rides trucky! I sold em cause the 13s are better imo.
Alternatively, you can still the hubs to accept a toyota six lug pattern, there is a write up on this forum about that.
But to answer your question, those adapters are a cheap, dirty way to go if you have a set of 4x100 wheels that you like already, but account for the change in wheel placement on the car, (offset?) that those will cause, and it will stress your suspension that much more, so those adapters should not be part of a beast off road build, but if it's something just for shows or your racing slicks, get back to us on your experience!
The adapters cost $160...you can five lug swap with junkyard pieces for that!
If you are considering going this route just to expand your wheel choices, i would go five lug swap. If you happen to have a 4x140 setup with rear disk brakes, don't change that, that's the old school cool right there!