In recent years Brother have introduced smart-chips to their ink cartridges, throwing a spanner in the works of refilling. Fortunately third party microchip manufacturers have produced compatible versions so that generic and refillable cartridges could be used.
We are still waiting for reset chips to fit to refillable cartridges and to replace the Brother LC-3217 and LC-3219 BK/C/M/Y. Compatible pre-filled cartridges are available, but are very expensive! So at the present time we recommend avoiding the MFC-J5330DW, MFC-J5335DW, MFC-J5730DW, MFC-J5930DW, MFC-J6530DW, MFC-J6930DW, MFC-J6935DW printer models if you wish to refill your own cartridges. Obviously this situation is subject to change, so keep monitoring our blog for updates.
There may be some retailers with remaining stocks of older models. In which case these will probably use the LC-223 LC-227 series ink cartridges. Compatible and refillable versions are available at a good price.