To the OP, as you can see there are many schools of thought on secondary vessels, and dry-hopping, as well as glass vs plastic.
There are many veteran brewers who only use buckets while others like only glass carboys, and still others are advocates for Better Bottles. It is similar to the Hatfield's and the McCoy's, the feud can go on forever.
Many here have had great success with dry-hopping in the primary, while others say it is a necessity to dry-hop in the secondary. Everybody has their own opinion how things should be done, and of course, some even think the way
they do it is the
only way it should be done.
One last thought that I wanted to share is that humankind has been brewing for thousands of years. In that time, many different fermentation vessels (size, shape, and materials) and techniques have been used. Although some practices have been proven to be better than others, It is my belief that on the homebrewers level that the difference between a plastic and a glass fermenter is negligeable. There are obvious differences between glass and plastic when it comes to such tasks as cleaning and secondary fermentation, as well as weight and size etc...
As long as your practices are consistent and sanitary, you can make excellent beer with either glass and plastic, whether it is a food grade plastic bucket, glass carboy, or PET Better Bottle, primary or secondary dry-hopping.
RDWHAHB, and enjoy!