I researched all types of food storage possiblities that would also allow freezer, microwave, etc. These were the best. The pyrex allows you to keep anything in it without staining (unlike plastic which quickly smells and discolors)...and then also to heat it up in the microwave. The only downside of pyrex is that it is breakable. I've lost 1 of 3 to breakage in the past year. However, the pyrex on the other two is still faultless and the lids in excellent condition. I make sure to avoid microwaving with the lids (with anything acidic, eg., tomato based) to ensure they stay in top condition. They have no stains after 1 year. Have also used in the freezer, with excellent results.
The last reviewer marked with down 2 stars for not being square, which seems insane. I never found the circular shape affected my storage options that dramatically!
Buy these with confidence. They only thing you will want are more and more...