I've never bothered - I can't see myself needing 7 digits, my highscore to date is 860,000 with five balls and A LOT of games to get it 
If I ever get 980 odd I'm tilting.
It does seem harsh to me that if you get multiball and then hit the six centre target arrows again you only enable one lock, so that part of the mod sounds good. I've never had two mulitballs in the one game, best I've done is a multiball then lock two balls.
Kind of agree, I find the balls drain really quick in multiball on this game - quicker than any other (except maybe BH), and I wondered myself if I'd actually be able to make use of the multiball mods so thought I'd see others thoughts.
