Do you consider a snap sampler to be a suitable low-purge sampling device?

Yes, I do.  As a matter of fact, even though snap sampler is not in any way associated with our company, I would have to say that from my knowledge of the literature as well as my own experience, the snap sampler is probably the most suitable no-purge sampling device, granted it's the most expensive.  There are other devices on the market that are no-purge passive samplers that are quite a bit less expensive.