While this works it is on the basis that the row count at the subscriber is supposed to be the same as the publisher. I have seen many cases where vertical and horizontal filtering is used on publications and the table at the subscriber is therefore significantly different from the publisher both in columns and in row count.

Have you looked at tracer tokens. These are simple to use and give very quick indication of any latency which can be investigated further and with the use of the underlying stored procedures very easy to set up to generate email alerts. There is also the dmv sys.dm_os_performance_counters which can be used to monitor latency and throughput.

These two features available within SQL Server are in fact simpler to use than your TSQL script and less of an overhead for very busy replication systems.