I cannot say that my flying skills have outgrown my V400D02 just yet, but my mechanical skills certainly have. Mine was a reliable daily flyer, but I had to initially mod the hell out of it--metal gear servos, brushless main motor, brushless tail motor, all of the associated brushless ESCs and converters, and COCO's superframe. I never had the lockout problem like Integrity did, my Rx2614V and even my Rx2702V have been pretty solid performers (though Integrity's posts do give me anxiety about lockouts
). Modding the V400D02 so that it would hover decently taught me a ton about heli mechanics, enough to build my own 450 Pro for a fraction of the cost of anything Walkera has to offer. Once you have that knowledge, there is no going back. I absolutely love the design of the 450 Pro--it really is a tough, well-designed heli, and I got sick and tired of the fragile frame design of the V400D02.
I do like my V120D02S, however, I like it a lot. It seems a lot like a mini version of my 450 Pro (I realize all the reasons why it actually isn't, but it just seems that way to me). I like that it is fairly crash-resistant, easy to repair, and the gyro works pretty darn well in the wind. But, right out of the box, I had to replace the Rx. Crashed the heli serval times before it occurred to me that the gyro was not working correctly, and by that time the vendor was unwilling to replace the Rx for me--that whole deal was very annoying! Once that was taken care of, though, the heli flies great!
At any rate, based on what I now know, I would never buy a large RTF heli from Walkera (or anyone else, actually). By 'large' I mean anything in the 200s on up. Modern day Walkera micros appear to be pretty good (e.g., Genius, Mini CP, and V120D02S), so I wouldn't hesitate buy one if I wanted another micro heli.