On Mi Band 2, after few months of usage the closing mechanism was very loose and I almost lost the band a few times. Mi Band 4 strap is a bit more robust and I don't remove it every day as with Mi Band 2 + wearing it "upside down" helps with accidental unfastening, but it still doesn't bring much confidence. So I bought 2 aftermarket straps. Short comparison:
- the all black one - strap is very soft and very thin. The Mi Band is very light, but the strap is even lighter and causes an imbalance - strap tends to rotate on the wrist. Closing mechanism is secure, but the buckle is hold only by two tiny pieces of silicone so I imagine that it can tear quite easily. Strap has protrusions from the inside (probably to hold it more securely on the wrist), but they dig into the skin. Overall execution is not very good. The only positive thing about this strap is that the strap keepers can be used on the original strap, making it much more secure.
- black/grey strap - this has a much better feeling. Good craftsmanship, ideal thickness, great comfort, very secure closing mechanism, nothing protrudes. Based on the reports from Aliexpress, the white plastic can tear off from the strap after some time (while removing it for the charging), but for the time being this strap is perfect.
- genuine strap - I wouldn't recommend it for active usage without strap keepers, but with them the strap feels very secure and I can't unfasten it without moving the keepers first. Except the closing mechanism I have no objections.
- the all black one - strap is very soft and very thin. The Mi Band is very light, but the strap is even lighter and causes an imbalance - strap tends to rotate on the wrist. Closing mechanism is secure, but the buckle is hold only by two tiny pieces of silicone so I imagine that it can tear quite easily. Strap has protrusions from the inside (probably to hold it more securely on the wrist), but they dig into the skin. Overall execution is not very good. The only positive thing about this strap is that the strap keepers can be used on the original strap, making it much more secure.
- black/grey strap - this has a much better feeling. Good craftsmanship, ideal thickness, great comfort, very secure closing mechanism, nothing protrudes. Based on the reports from Aliexpress, the white plastic can tear off from the strap after some time (while removing it for the charging), but for the time being this strap is perfect.
- genuine strap - I wouldn't recommend it for active usage without strap keepers, but with them the strap feels very secure and I can't unfasten it without moving the keepers first. Except the closing mechanism I have no objections.
