The Biofuse fins are an excellent addition to speedos other biofuse products (i have the paddles too). The fins are well made and provide good power when you kick in the water. They are ideal for strengthening your lower core muscles and thighs. The fit on my fins is good, I am a EU 42 / UK size 8 and bought the overlapping EU 41/42 size. They are a good comfortable fit, with no tight spots or anything flapping loosely. The fins had an unexpected benefit of allowing me to improve my backstroke which is weak. By having a more efficient kick, I can more easily maintain good posture in the water and focus on my arm movements and head position. The fins give a good workout especially over 500 to 600m. The fins have useful tangs on the top to allow you to grip the fin when pulling it on. Here is some simple tips on using these fins - firstly put them on in the pool - they go on better when you and the fins are wet. Secondly when putting them on, slide the fin over your foot then pull them up your foot by holding the front of the fin and drawing it towards you. This ensures you foot sits well within the fin and makes it easier to pull the back of the fin over your heel. When using the fins kick from your thighs and core and not from your knee.