Just a quick comment.
anyone who has a modified sine invertor.
Plug your pc into the mains, and check the temperature of the PSU. Then do the same with the invertor.
You'll find that off the invertor it will probably run very warm to hot in comparison with the mains, some PSU's even "sing" when running off an invertor.
The problem arises because both the invertor and the PSU are both switched mode power supplies, and the harmonic noise from the invertor "annoys" the computer PSU (different switching frequencies).
Anyway, The Opus is cheap enough, buy one, they work!