I'd take the general consensus of BB.COM with a grain of salt or dextrose
Creatine causes INTRAMUSCULAR water retention, not the bloat that is generally associated with creatine supplementation.
This is generally what happens, creatine is used by bro's on their 'bulking' phases. But what happens on their bulking phase is their carbohydrate intake goes up, overall calorie intake goes up, sodium intake increase (unknowingly) and then they are carrying all this 'extra water' or are 'bloated'. What gets the blame, good old creatine.
Also, there are a lot of 'creatine' products that contain some form of carbohydrate and a large amount of it, think Cell-Tech. Now last time I looked at the back of Cell-Tech, 70%+ of the contents where dextrose! You want water retention, Oh I mean you want to gain 7lbs in 7 days you got it
Yes there are non responders at that is about 20% of people. Why? Well it is not completely known but it would have to be something to do with the mechanisms involved in uptake and/or ATP cycle IMO.
Amount of benefit? well that is hard to pin point as there are many other intangibles and variables that effect training performance/ability/muscular hypertrophy. You may get an extra ~5% out of your training over time if you are doing EVERYTHING else right.
Here is some reading for your leisure
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Effects of creatine supplementation and ... [J Strength Cond Res. 2003] - PubMed - NCBI
Effects of creatine on isometric bench-... [Med Sci Sports Exerc. 2002] - PubMed - NCBI
Effects of creatine supplementation and ... [J Strength Cond Res. 2007] - PubMed - NCBI