^ Yeah, the phased cloak is actually two-for-two in nearly destroying any ship that tries to test it. Later experiments probably proved even more problematic, thus leading to their abandoning the research.
There's only one thing about this treaty that ever bugs me, and it's this: the Romulans do not object to Starfleet USING cloaking devices (the only reason an observer was necessary was because the Romulans had loaned them one of their
cloaks in exchange for their promise not to use it in the alpha quadrant and share their Dominion data). The treaty forbids their DEVELOPING cloaking devices. There's really nothing in this treaty that would preclude Starfleet buying cloaking devices from the Klingons, or even asking the Klingons to develop one specifically FOR them. Moreover, there's nothing to forbid Starfleet from using holographic technology to camouflage
their ships as something else; that much we already know was possible even in the 22nd century, and even better mastery of holographics and sensor trickery would probably permit a perfectly viable forgery for a Starfleet vessel that wishes its identity to remain anonymous.
Missed opportunities all around.