There's nothing inherently wrong with BLX or even PGX mics. They work fine if deployed properly, there's just not a lot of versatility or control available if you are trying to navigate very complex RF situations. The design assumption is that users are unlikely to be using more than 2 these systems at a time, and they will be indoors at relatively close range.
To get a dozen or more of this mic class to work simultaneously requires some serious RF planning and care. One of the most common areas for this problem is school and community theater. Here, the budgets are low but the number of people wearing a mic and the subsequent expectations are high. A parallel situation occurs when there a multiple DJs working within a multi-room event space like large hotels or conference centers. DJs tend to buy similar modest level gear which is also consistent with gear used by restaurants/bars and other hospitality services. The odds of multiple entertainers and hospitality workers stepping on each others RF increases quickly in busy commercial areas.