I actually mark the track at 10m intervals from various positions so that we don’t have to worry about that. For tempo (which I usually don on grass), I measure with a wheel the first time and then just count steps after that. My steps are ‘calibrated’ to an accuracy of about +/- 2m / 100m which is acceptable to me. For testing purposes or if you’re going to be using timing gates regularly though you’ll definitely want a good tape measure.
I have a wheel also but the tape is much easier to transport around to different training sites etc. I agree, I use to count steps after using a measuring tape and never had a issue with being accurate. The 30m tape only cost $15 with free shipping, sounds like a decent deal.