I don't know the mics in question so I can't comment on that but in general I'll try an Omni dynamic anywhere I would use a cardioid dynamic. I have a few different models that I like on specific things - an Altec/Western Electric salt shaker has been pointing at the snare drum of my house kit for a few years now.

- They can be a great second or alternative mic on guitar amps (especially great for variety when you double parts).
- I sometimes like them on acoustic guitar.
- Drum room - try them on the floor out front of the kit.
- Heart/Crotch mic on drum kit is a great application. I'll sometimes put a 635a here and run it onto an overdrive pedal on the way to tape.
- under snare can also be a good spot provided you want some kick attack in there as well.
- They can be fantastic fo percussion and hand drums.
- They can also be nice on the back of an upright piano or inside the case.

They will pick up more bleed and room tone than a cardioid mic but the lack of proximity effect means you can place them very close to the source. On something like a guitar amp in the same room as a drum kit the source sound to bleed ratio is a non issue (for me at least).
Bleed is more of an issue when when close micing drums and with the exception of the salt shaker on snare I generally use omnis in a place where they're hearing the whole kit (front of kit, OH, room, heart/crotch etc).

There are several copies of "Microphones - Design & Application" by Lou Burroughs available on eBay. Most are "quite pricey" -- but as of this writing, there is a new listing for a used copy, and the starting price is something like $3.99, but the seller wants $11.80 to ship it.

I do have this book, and it is extremely informative. Burroughs is, indeed, a big believer in omnidirectional microphones -- for a lot of excellent, logical reasons.

The auction for this particular book is slated to end on 11/17.

I tried two Sennheiser MD 211 on grand piano and liked the results.

Can't blame you. That sounds ace. Vibes.

The MD 211 *is* really one of the best dynamic omnis around.

Thank you @ Karloff70 and @ John Willett !

No, actually, for anyone considering buying some now, these are complete crap and not worth much......

There's just something about a real piano, that even on my MBP speakers, I could sense immediately. Beautiful recording.

Here's a few ideas:
- Spaced pair in a reverb chamber (just make sure there's no direct sound reaching the caps)
- as has been said, stereo "inside kit" drum mics
- get a 3rd omni - needn't be the same model - and set up a Decca tree, with the 3rd mic in the center. For drumkits / percussions/ small strings or brass ensembles.
- recorderman drums
Also: this may prove useful...

I’ve been tracking drums with an old Radio Shack omni as a crotch mic, running into a distorted amp in another room. Blending it in doesn’t sound as weird and phasey as when using a 57 or other cardioid. The mid-fi quality of the mic helps roll off the freq extremes nicely too.

This is a big sleeper, Lanier made a version as well, it's a rebadged 802, and I think mine was $20 shipped. I've picked up several random dynamic omnis here and there.

Now I need a pair of 802's too!

I got a green bullet mic to play blues harp with. Was surprised since it's omni and the above comments make sense. I was worried about feedback cupping the mic but a very forgiving mic for lack of a better word and really fun!......

Since we're on the subject of omnis ...

There's nothing like the natural top-end clarity and overall accuracy of the "flat" EV omnis -- the RE55 and DO54/PL9 ... the latter two being the same except for the case color -- and all three have the same omni element. The RE55 has better bass response.