The Yuin PK3 is traditional earbuds, not an IEM.
The Sennheiser MX300 is not worth the price. The CX300II is said to be very similar. I have the CX300 and don't use it much anymore.
In the under $25 range I like the Panasonic RPHJE450, JVC HAFX40 and Panasonic RPHJE355. Imo all these are better than the CX300 and cheaper. I use these with my Clip+ and Clip Zip. The HAFX40 has the most detail, however it is quite bright. It needs plenty of burn in. Let it play 24 hours a day slightly loud for a week before using it. It also has good bass. I am starting to get more used to the Sony MDR-EX210. It has 13.5mm drivers and strong bass. Sony describes it sound as rich. I describe it as thick and slow. It is quite pleasant to listen to, but compared to the others I mentioned it seems to be missing detail. It does have a very laid back smoothness to it. I guess I am getting used to it.
I like the fit and the comfort of the very ergonomically shaped Panasonic RP-HJE450. It has 12.5 mm drivers, nice bass slam and good detail, but not as much detail as the HAFX40 or HJE355. It is the IEM that I use the most. It is ported though, so isolation isn't so great.
The HJE355 has less overall detail than the HAFX40, however the HJE355 seems to have a much better midrange and is slightly warm. The HAFX40 is very bright and has a U shaped response.