I installed mine and not only was it crap but the speakers developed a short within the first days use then the amplifier stopped working after the third trip (possibly both related to the speaker fault)
I ripped it out and installed a Sony HR70 with a couple of good speakers, the whole lot cost only £20 more than the Poly planar and the difference is night and day, plus an AM/FM radio and a CD player are included. And the CD works perfectly when bounced about as well.
The music is still good enough to sing along to at 25 knts and almost full throttle.
If you have the space I would go for one of these, if not I would still go for one and mount it inside.
On the way across to IOM we WILL have music and so will everyone else whether they like it or not............