I went 6 yrs without one and never had a tire with low pressure. Added a TST 507RV last year. Still have not had a low tire.
But I really like the ability to monitor tire pressures and temperatures during a long drive. It is not unusual for me to drive 2-3 hours without stopping. If a tire picked up a nail shortly after starting out I could easily end up with a ruined tire within a few miles and, if it came apart, possibly damage to the RV. If a tire pressure drops below a certain set point or develops a rapid leak the system will alarm and I can pull over before it is ruined. Will not prevent a sudden blowout, but could definitely save ruining a tire on a slower leak.
Based on my experience I would recommend the TST 507RV system. It does have user replaceable batteries.