I have the portable PI 50A version since 2007
It tests power on both lines, tests neutral, tests ground, has Hi/LO voltage trips etc etc
Got it because we had a new RV and were hitting the road FT and would be using numerous unknown power sources.
Over the years it has detected
Loss on neutral, loss of ground, reverse polarity, has dropped connection due to low voltage on several occasions, a mis-wired pedestal
Was it worth the cost?
Kinda like Insurance......only when it was needed. And to late AFTERWARDS.
Unlike insurance which costs every year it is a one time cost
PI has LIFETIME warranty and stands behind it (TRC---limited 1 yr and so-so response)
Worth it.....only need ONE messed up power pedestal source and could costs 100's or 1000's