Metal cassette's and bias settings?

Could someone tell me why bias controls don't have much affect on Metal type IV cassette's,and is it true that TDK tapes don't last as long or hold onto there music as long as Maxell cassette's?And are TDK's more prone to dropout's and loss of high frequency than are TDK over a shorter period of time ?This is just what i have been told before and i don't know,I was told to never put anything that i don't want to lose on a TDK cassette because after about 5 years or so there start to exibit the above problems..Is any of this true or is it just "hogwash"? Thanks for any help,Keith..
If you want to buy any blank metal tapes, I recommend that you buy them soon. I don't think many are being made anymore. When looking for blank TDK's a few months ago, I learned that my local stores stopped carrying them, and most web sites no longer had them. Did not run across many alternatives either.

I think that medium is dying; especially the higher end cassettes. Perhaps some Agoner's can shed light on some sources ?
I've had a few TDKs go bad, never a Maxell. I have tapes that I made as far back as the 70s. I would go with Maxells if you can find them. I used Type II & Metal only. The old Sony UDXL Pros were nice also. I feel the Maxells keep the sound better over time than TDKs also.

Actually I always used Maxell XLIIS not regular II & TDK SA-X. You can get the Maxells on E-Bay most of the time.

Maxell tape has always had a better binder and calendering system than TDK did IMHO. Sonic wise I like allot of the TDK tapes better, but the Maxell UD-xl-2 were a fav of mine. Having a Tandberg 3014,Nak ZX-7, and various decks from JVC,Teac,Sony es, etc., I have run the gamut of different tapes and such. I use a Tascam 122 mk.3 now because it sounds decent, the support when ever it breaks is superb. I used TDK open reel tape with great satisfaction and liked them better than Maxells. Cassette though for the long run, bias and eq. for Maxell of your choice and be done. Happy taping.