I think the system works pretty well. If it's marginal, then on review, the decision stays as the umpire call on the field. The reviewing team don't lose their review and the game carries on.
This new system isn't restricting the scores, so batsmen aren't being unduly hampered by it.
It has also stopped batsmen hiding their bat behind their pad and pretending to play a shot and running down the wicket to kick the ball away as umpires never gave them out, whereas hawkeye can. This is turn has made umpires much more likely to give them out as a result.
It's amazing how many correct calls the umpires make. The umpires call element of hawkeye is minuscule if you look at it from where the umpires stand, yet 95% (my guesstimate) of their decisions are accurate.