I live in London, UK and work for a TV company that produces shows for PBS
in the US. I have never had any problems here playing NTSC discs.

They do look a little softer than PAL ones, since the picture is stretched a
little but not so the average user would notice. The only problem that might
crop up is if someone is using such an old TV or monitor, and we are talking
very old here, the picture could play in black and white.

The reverse isn't true - we have had lots of issues with PAL discs being
sent to US clients and being unplayable.

I am sure you know this but just in case not there is one caveat... do not
add any regional code! Almost every TV professional I've worked with still
confuses regional codes, region 1 for US and region 2 for Europe with video
formats NTSC and PAL. If you do add a region code then you will find discs
will not play!

Make your discs in NTSC and region free and you should be fine 99% of the
time!