I have a similar one. In fact if you google the words Pentax and intervalometer you will find other very similar units. The prices vary from $15 to about $80 from a variety of vendors (probably all the same manufacturer in China).
Mine works very well. The only comment I would make is that mine does not have an on/off switch, but it appears to not affect battery life. All the Pentax bodies have the same Canon type jack, so it does not matter K100 or K5 or ?? Mine fits both my K100 and K5 along with the K20 I just sold.