[Elecraft] K3 External Frequency Reference Questions

[David and Dianne on Comcast]

Hi All,

I'm interested in possibly trying the K3EXREF in 
my good ol'  K3 for no good reason other than its 
something new and fun to try and can give some 
bragging rights about frequency accuracy.  Can any 
of you comment on your experiences in using the 
K3EXREF? Elecraft provides very little background 
info on how to get started with this accessory 
after its installation.

I see that the once prolific Trimble Thunderbolt 
units are now quite scarce on eBay and elsewhere 
those that are available are now really pricey.  
What are any of you now using if you went the GPS 
disciplined oscillator route?  Have any of you 
used a rubidium standard as the alternative?

This may sound naive, but is a rubidium standard 
device safe to have at home, i.e. is it 
radioactive? I think I know the answer but I want 
to ask anyway. With a toddler grandson around here 
often I want to be very safe and very certain.

Any suggestions as to how to proceed, encountered 
pitfalls and sourcing a reasonably priced 
frequency standard would be greatly welcome.

I thank you all in advance.

73 de N1LQ-Dave