I do RF PCBs requiring micro strips etc. It must use double sided FR4 boards with consistent permittivity and very accurate trace thicknesses for impedance matching or inductance chokes.
The hackaday technique assures such results repeatably.
All acids must be handled properly, I have 30 years experience with conc. NITRIC and never a problem. HCL is also dangerous, fumes, and can emit large volumes of chlorine if it comes into contact with household ammonia cleaners.
http://www.flinnsci.com/media/396140/acidsafety.pdf When nitric is etching copper it bubbles a bit and self stirs the mix for cleaner trace edges I have found. Also the fine even bubble generation reveals any improperly cleaned copper areas within a couple seconds. Such areas can lead to longer immersion times which will cause over etching of the properly cleaned areas. In effect it gives me quality control feedback that other etchants don't.
Further, the copper nitrate end product is beneficial to sewer systems for restricting root growth, a fungicide or as a soak for preserving outdoor wooden surfaces.
- Cupric Nitrate (Copper Nitrate) Cu(NO3)2·nH2O, green powder or blue crystals which is soluble in water; used in electroplating copper on iron; as a catalyst and nitrating agent in organic reactions; component in rocket fuel; fungicides and wood preservatives; textile dyeing and printing; pigment in ceramics;