I have a 70L tank like you (low tech, low-ish fish load), and I upgraded about three or four months ago from an annoying hang-on-back to
this external filter from All Pond Solutions. I am pretty happy with it so far. It puts out a flow which is just fine. Build quality is reasonable, it came with decent instructions, all the hoses and fitments, and a variety of sponges (and some balls which I didn't use). Spare parts are also available separately should that be required. I chose this external filter 'cos it's not super expensive but it definitely feels like a nice upgrade over my old HOB. I know it's not Fluval or Eheim or Oase etc so I can't comment on longevity.
In addition, I made a sponge 'sock' for the end of the filter intake inside the tank. A bit like the sponge block Darrel recommends except mine is just flat filter sponge sheet sewn into a cylinder with a flap to close the end, all secured together with some fishing line. Each week I slip this 'sock' off and squeeze it out under the tap as part of my water change routine. The 'sock' stops the sponges inside the external filter getting blocked by debris which means that I have not opened the external filter since I started it and the flow is still as strong as on 'day one'.