It can, it will certainly increase the flow to a hot (only) tap, if the shower cold supply is from a CWST then despite boosting the hot supply the flow will probably not increase much as the mixer will throttle in the hot to enable it to mix with the lower pressure cold, if the cold is mains supply then the flow rate should improve but I don't think TMVs work with a high difference in hot/cold pressures (> 1 bar?) but your shower may have manual mixing controls anyway.