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I have had this wireless keyboard & mouse set for over 2 years - originally bought from Tesco priced at £19.99.
Both items came with Duracell batteries and Microsoft say that under normal use batteries should last over 6 months... however I later found out this to be inaccurate. There was also a PS/2 to USB converter for those with older computers.
Initially I was very impressed with the way the keyboard and mouse felt. The keyboard is slightly curved and the keys are well spaced out; both combined makes for comfortable enough use over long periods. The top functional buttons work right out of the box and does not require additional software to be installed.
The mouse feels good overall, the motion is responsive and as it is weighted by batteries is perfect for moving over a mousepad or flat surface. Clicking felt intuitive and the sound was a dulled note rather than a sharp click one would expect - great if you do a lot of clicking during night time ;) and the middle scroller is equally silent. So it scores good for ergonomics and sound.
However, I really disliked the mouse and keyboard for various reasons. Firstly the keyboard sometimes gets stuck - in the sense that when you press a key it doesn't register and you need to repeatedly press it. The space bar is a little springy and does make a reverberating sound when tapped. This is also the case for the Return/Enter key.
The mouse equally has its flaws. After only using it for 2 months, the top layer of paint/coating came off as did the Microsoft branding and before long the mouse looked like a misused junk which has been abusively scrubbed with those metal dish cleaning equipment (for lack of better words).
Furthermore, signal strength seems to be very poor and at about half a meter away from the receiver, both mouse and keyboard seem to fail to register clicks or keys. I have had to at numerous times reset the keyboard, mouse and the receiver in order to have it operational again. Occasionally I have had to bring the receiver right next to the keyboard and mouse for it to work. More annoyingly the set would sometimes work just fine and all of a sudden stop working properly.
Overall for all its design, comfort and price, I cannot recommend the product because a keyboard and mouse should be about usability and more often than not the product has been absolutely unusable.