Spectrum typically charges an equipment monthly lease fee, including a fee for the remote control, and if wifi is to be activated in their modem/router, there’s a charge for that too.
Unless these fees have changed recently, that what it’s been like using their equipment in the past.
I normally prefer and generally suggest other spectrum internet users to get their own docsis modem and quality router.
@Thatguy - That being said - I’d suggest as @Powerfader mentioned, to have your friend test the connections using his z11 ethernet port and see if problems persist. Does the buffering in the streams only prevalent when using his iptv service. Does buffering occur with YouTube, Netflix, Amazon, etc?
Some iptv providers are unpredictable with when they perform well. This depends on server load at the time, what node each connection is using at the time, the internet providers hop performance (test by using tracert) between end to end connection.