What are the advantages to a Class A amp & what are the trade offs?

Very interesting thread. All I can say is I recently bought a pair of Class A 45w SET monoblocks that greatly improved my system. Built by Vlad of Audio Mirror. I never had monoblock amps or an SET amp so I took a chance. I did not get them because they were Class A design, but because they were SET and I have always been very curious about SET amps. They have a very uncolored, neutral but natural sound. Cymbals sound like..well, real cymbals. They are open, clear space between instruments and voices, yet very organic, dynamic and sound very effortless. When I listen to music I hardly adjust the volume. You hear detail, background at whatever volume is present. They run very hot but my room is very cool in summer so it’s not an issue. I could care less about the power bill...you only live once and can’t take it with you! They seem a perfect match for my Egglesston  Works Fontaine Signatures. Thx again for this thread. Always something to learn here on A’gon!

jdl57 those amps are the nuts!  An other classic John Curl design. Back in the late 70s we had 8 of them driving the ML HQD system, one on each Quad, Harltey sub and Decca ribbon tweeter. 200 very expensive watts and boy was it impressive back them both sonically and visually. The Hartleys were in infinite baffle enclosures! 

Excuse me, but what is an F5 amp?  I can't find it in this thread.          I found excessive global negative feedback is also not my preference.  I like the VAC Class A/B amps with 6 db of same.  

Wasn't the XA25 the amp with superlative technical reviews?  Thanks for the info.