You wont feel anything but you will hear a drone. Will be next to impossible to determine which wheel it's coming from but it's also relatively cheap and easy to sort. Bearings are something I'd use genuine parts or at the very least a decent brand
The rear hubs are a complete sealed unit so you can't just replace the bearings. Genuine Ford are about £250. I replaced mine the first time with a pattern part from Ford that cost about £80. It lasted about 12 months, cheap £30 ones off Ebay lasted about the same.