Prop Firm Spreads and Execution: Is There a Hidden Catch?

Been giving some thought lately to the actual trading environment offered by various prop firms, beyond just the challenge structure. Specifically, I'm talking about the spreads and execution quality once you're funded. Many firms advertise access to 'raw spreads' or 'ECN feeds,' but my experience, or rather, my concern, is that the execution isn't always what it seems.

I've seen situations, particularly around news events or during less liquid hours, where the spread widens significantly more than anticipated for a true ECN feed. This isn't just about a couple of pips on $EURUSD; it's about the difference between a profitable setup and a stop-out because your entry/exit was compromised. My question for those of you who have been funded with different firms for a decent period: have you noticed any consistent discrepancies in advertised versus actual trading conditions, especially regarding spread widening and slippage? Is it just market conditions, or are some firms less transparent about their true execution environment?