has anyone used the lmf40,lmf60,etc

[joseph s ramstrom]

Hi all, I was paging through the national semi data accuisition book and 
found the lmf40, lmf60 4th & 6th order butterworth low pass filter.  
packaged nicely with two spare op amps, one nicely biased to ground(lmf60).  
controllable with either cmos clock or voltage adjust(res cap combo) for 
the cutoff frequency.  

Are these too good to be true? 

Has anyone one the list tried them out?

also if any one can tell me about the other chips that national has such as 
the lmf90 notch filter  and lmf100 triphase (my memory is fading on the 
lmf100 so thats what I think it's called).  Any advise and experiences 
would be helpful thanks.

joe ramstrom