I've been browsing obsessively for several months on an engine analyzer for my Decathlon. A full functioned monitor approved for primary gauges is awfully appealing. Examples would be CGR-30P or EDM-900, or MVP-50P if money is no object. If you want to save some $$, the EDM-830 does all the same things but not as primary, so you have to leave your steam gauges in. IMO the CGR-30P is the best bang for the buck, and fits in a large gauge hole.
I have a 1978 Decathlon with original fabric and wood spar, so it doesn't make sense to install an instrument worth 5-10% of the value of the airplane. I also have a low panel without much extra space. So, I've narrowed my focus to lower cost options that fit in a 2 1/4" gauge hole. Right now I am looking at 2 options:
Insight G2 4 cylinder EGT/CHT with fuel flow and data logging for $1900.
Aerospace Logic ECT204 4 cylinder EGT/CHT for $1500, combined with EI
FP-5 Primary fuel flow and pressure for $900. I really dig the display on the ASL, so probably leaning towards that.
Any piston aircraft can be leaned reliably. LOP vs ROP is a different discussion. People I trust who know way more about airplanes than me have told me to resist the temptation to try LOP, so I follow the factory instructions in my AFM. Can't go wrong with that.