Generations, over the past few years, have indicated some serious quality control lapses at their point of origin. It is a rare Generation that will play decently without a modicum of "tweaking". There are some "Pro" Musicians who swear by them, but I will stick to my Clarke "Traditionals" in "C" and "D". I have heard rumors that Clarke was going to expand into other keys, but these have not been forthcoming much to my disapointment.
One trick with the wooden-plugged Clarke is to sand the exposed end smooth and soak it with mineral, almond or sesame seed oil. This will prevent it's swelling and shutting down the fipple as it gets wet from playing.
I picked up a little "F" Generation on a lark, and got it to play reasonably well by slightly blunting the windcutter blade with a strip of emery paper, filling the cavity behind and under the window with candle wax (dripping it in, then forming it while still warm & soft with a coffee-stirrer stick) and trimming the mouthpiece back about a quarter - inch and angling it downwards to facilitate tounging.

There are a few ways to "cheat" on tuning a non - slide equipped whistle: trimming a little off of the end will sharpen it, but will also throw intonation off if overdone. Sometimes a bore reducing constriction right at the muzzle will flatten the tone and add a certain resonance. I stuck a 5/8" brass gas line reduction flange on the end of my 3/4" brass tubing "low" whistle (salvaged from a floor lamp from the dump) to good effect. Your hardware or plumbing supply store may help you come up with a suitable fixture at a modest price. If you masking-tape over the tone holes and slowly roll a fingertip over the muzzle while blowing the base note, you can hear this effect and get an idea how much constriction you need or can get away with. I have been known to roll up a little strip of paper and stuff it up a whistle's nose or cover a wee bit of it with a smidgion of duckt tape - not a particularly aesthetic modification, but occasionally effective.