There is a huge amount of difference in the performance of an industrial filter and a true music filter used with custom moulds. Music reproduction requires the attenuation response to be flat across all frequencies, whilst the attenuation of an industrial filter typically rises as frequency increases e.g. from 12dB to 28dB therefore giving poor music reproduction. Industrial filters are normally a resistive design being little more than a restricted tube or hole, whilst a music filter can have various types of membrane, chambers etc to provide a flat response then tuned to compensate for the ears natural resonance at approximately 2.5-2.7kHz, resulting in a flat attenuation response for the user.
Foam plugs certainly reduce the noise level very effectively but score a big 0 for music applications.
Numerous companies make custom mould hearing protection, the combination of the custom mould and the filter being the 'product', it's this product that is certified; objective testing of the protective performance. Like everything to do with music reproduction subjective testing can have different results. I should point out that 2 custom mould manufacturers could use the same filter but have differing performance, this is due to the canal design, shore hardness, fit and sealing in the ear canal.
Hope that helps and notice that no companies were hurt in the production of this reply 