I have heard that a drawback to tankless heaters is the inability to control temperature at low volume. For example, the water will be too hot when using a single faucet to wash your hands. Has anyone heard about this?

Yes, homeowners complain about this frequently.

Because the water in a tankless coil sits inside the boiler,the water will reach the temp of the boiler water. Most plumbing codes require a tempering valve installed on the boiler. This tempering valve allows cold water to be mixed with the hot. The valve has an adjustable temp. Tankless coils are ok for single people. If more than perhaps a super store water tank will help. It uses a zone and a circulator pump to heat water in a seperate tank. I plan on installing one this summer. Cost varies but a good tank could run 600.00

Shue, confusion follows because most posts today concerning instantaneous water heaters are called tankless heaters. A tankless boiler applies to your commentary; however, it is most likely that this post was about an instantaneous wall-hung water heater without pumps (not a home-heating boiler.)