The G&L MFD pickups are extremely sensitive to strings. My L-2000s have worn a wide variety of strings, including flats, but I always keep coming back to either GHS Boomers, which were what the MFDs were originally designed around. I used rounds on my first L-2000 for 15 years and there was barely a mark on the frets when I sold it. I think you're being a bit absurd if you're limiting yourself based on saving a little money on fretwork 20 years down the road.
Edit: My L-1000 recently got TI Jazz Flats and I love them on that bass. It lets me really run it a lot more wide open and I can spend a lot less time tweaking the bass and treble controls.
Edit: My L-1000 recently got TI Jazz Flats and I love them on that bass. It lets me really run it a lot more wide open and I can spend a lot less time tweaking the bass and treble controls.