I have used coils from White's and most other after-market offerings, and have employed them beyond the woodchip playgrounds or around trashy picnic tables. They have been taken into torn-up sidewalk and street repair, and iron nail infested renovation in parks and schools. Worked around building demolition sites, and vacant lots where old structures stood long ago. Mounted them up for serious hunting around old groves and recreations sites, swimming holes, homesteads, military & pioneer encampment sites, mining camps and logging town sites, and ghost towns from deserts into the mountains. heck, I've even enjoyed just leaving them mounted to the working end of the rod for day-to-day hunting in open grassy lawns and sports fields, or hunting private yards.
I've used these smaller coils on an assortment of models including the 4 DFX's and 4 MXT's and 2 M6's I have owned. In all applications I have looked for a pleasant blend of comfort, good trash handling, reasonably decent depth for the physical size, and quiet, responsive performance.
I will tell you right now that I am, and always have been, quite partial to round search coils rather than elliptical, and I also usually prefer a concentric design to a wide-scan (Double-D) design. Having stated that, and after noting the types of sites I tend to hunt, here are my favorite smaller-than-stock coils for the M6 and MXT in order of preference.