Anyone not yet convinced of the merits of Lucas's iPhone app and the (optional) gizmo, I vouch for the combination. The adapter arrived in the morning post and I spent the evening testing my my Yashica-D and FED II shutter speeds.
Results from the iPhone app were very consistent. Unfortunately, while consistent, the accuracy of my Yashica was a sad affair. The FED faired better, 100th was spot on. The results for the Yashica TLR reflect with my film exposures, unfortunately!
So, simple, quick, accurate and not going to break the bank.