If you are looking to reduce the gain a bit,yes they are worth it.I have 17 amps in my collection and every one has a 5751 in the V1 position except one that has a 12AY7,which has even less gain than the 5751.I love them.I would say just about any NOS will do,I have about 15 backups in my box all different brands,and I like them all.The ones with the triple mica are obviously more durable and less prone to microphonics,but to tell the truth I have only found one microphonic 5751,as opposed to the many microphonic 12AX7's I've run across.They tend to smooth out the overdrive in my IIC+,dont have that harsh shrillness you get with most AX7's.I wouldnt recommend the current production 5751's,to me they sound like weak AX7's.