With any kind of development tool, you have to know how it works and to what extent it can help you. If Alien, for instance, does not prove to be sufficient, you have to fill in the gaps with other tools or even "manual labour".

Personally, alien, rpmextract, deb2targz, have all been useful. There's nothing on it that warrants recommendation because there's no other similar utility (at least not that I know of) - you use it if you need it.