The decision between dual or single-sided printing needs to be entirely based on what you plan on using your printer for. If you only need to print on one side of the card as you have a simple card design and are happy with the reverse remaining blank the answer is quite clear, a single-sided printed would be more suited to your needs. Single sided printers are ideal for ID cards that are being manually checked and do not require a magnetic stripe to be swiped through a reader.
Whereas, if you’re looking to print more complex cards, with information and text spreading onto both sides, a dual-sided printer would be best. The benefit to this is that you have the flexibility to utilise more space on both sides of the card. Dual-sided card printers are usually used for cards requiring many data fields and cards that require a magnetic stripe or area for signature.