I've bought both second hand (usually from this forum) and new NV and thermal, as someone already said, it would depend, only time I've had a issue with second hand, was a Pard NV007 from ebay, it was shown as working before it was sent, however never worked for me, which put both the seller and I in an awkward situation, which did get resolved amicably. With new you do get the security of a warranty but also the cost, there are however so very good deals to be had, also worth keeping and eye for new models coming out and dealers moving new old stock at good prices