We have a pair of these, we are on clay soil and they are quite hard work if you have a big lawn as we do. When it is wet, they tend to stay in the lawn and the straps to hold them on are not the best, ours keep coming loose so you end up trying to walk while the shoe is left stuck behind.
When it is dry of course, on clay, there is no way they penetrate. You have to have the perfect conditions for these to work, not too dry not too wet, and even then, as you say, your legs really ache afterwards. We have since invested in a bit of kit from the garden centre that takes out about 5 plug holes at a time, (it was £24.99) and then sweep in some sand, still hard work on a large area but at least you can do a bit at a time without becoming totally worn out. Good Luck.