Out of curiosity, do they give you a proper design file from their Ai builder? 'Proper' being ideally a Solidworks or equivalent file, but even a dimensioned vector file would be OK. I've never used sendcutsend, any time I quoted parts they came back more expensive than my local shops, but I do like the business model they have and it seems like a cool service.

I wasn't able to find anything about output files in their FAQ, and making a part in the AI builder didn't give me any answers unless I wanted to go all the way through ordering.