We use 5 Line 6 mics together and have had decent results-though my experience is that a WiFi router will take interfer with the mics. The real headache is the failure mode-they seem to be fine for a quick check-but when someone starts using it they drop out. Anytime a new router/access point is added in the room you'll need to verify reception. We wound up going to 5 ghz for mission critical wifi and hope no one gets too close with a hotspot.
A staff member purchsed some GLDX mics because a "sales technician" told him we shouldn't add more Line 6. The GLDX were unusable-constantly dropping out and re-linking.
The Sennheiser manual says "up to 15 systems in an optimal situation". In this day and age when will that ever happen? No WiFi, no hotspots no bluetooth in the room? Another red flag to me is in the troubleshooting section, dropouts can be caused by holding the mic wrong-so now I have another item to train talent on and butt heads over? Also, the GLDX would try to relink any time the mics got within 6-8" of each other.
We use the Line 6's with the factory jumpers for antenna's. For up to six systems, I might be OK with a 2.4G system, but I'll fight to keep any more out of our system.