The flight and ballistic models did it for me. After flying DCS and especially ROF lately WOP's fm just feel a bit too odd. The terrain and cockpits are very lovely though.
I don't mind paying for extra stuff, Maddox, ED, Gaijun, Neoqb are all small teams trying to produce stuff in a niche genre that I enjoy. If they produce quality stuff I'm happy to support them, and I do regard WOP as a good product I just prefer ROF.
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WAS C2D 8500 3.16ghz, 285gtx 1gb, 4gig ram, XP NOW Win7 64, I5 2500K, SSD, 8Gig ram, GTX 570