Hi Kooz.
First of all - the word "warm" is violently abused in the plug-in field. The sonic effect of "warming" is rooted in a lot of things and if a plugin claim to warm things it is just altering the sonic balance (basically eq:ing) and in some cases add harmonic overtones.
So, the word "warm" should really not be used at all, it's only a hoax from the beginning of audible life.
The products you mention are of different spices. If you use them in a veeerrry good monitoring environment (speakers and D/A) you will most likely find out that what they create should be used very gently. If your monitoring chain is lo-fi it is VERY easy to tempt yourself into creating something that does not sound cool at all.
The PSP does have a more mid frequency tilted approach. It creates quite a lot of grain and have a bit of analogue spice to it (much depending on that the lows and high is somewhat compressed). It is very easy to over-use it but it is also much harder to decide when the limit has been passed.
The warmifier is of another kind. It is very subtle and behaves more like good analogue valve gear. Even in a rather poor monitor environment you will hear when you have passed any limits with the warmifier, because it start to behave a bit nasty. So the effect of the warmifier is much more subtle than the PSP, but on the other hand it is much more nice to the over all frequency spectrum.
The PSP has got better dynamic controls and you can basically use it as a compressor, multiband compressor and even as a mastering limiter. The warmifier has not any of these adjustable parameters.
The warmifier on the other hand can alter the harmonic contents behaviour more than the PSP does.
The PSP has got a transformer-sound and the warmifier has got more of a valve-sound.
My monitoring chain is a Lavry Blue D/A into a pair of PMC TB2S speakers. Fairly good and very neutral. When my monitoring set up was more lo-fi I went a lot for the PSP. When I now hear a lot of what the plugs actually do to clean audio, I have to say that the warmifier is much more gentle and do less harm than the PSP do. Since I upgraded my converters ans speakers, none of these plugs are in my mixes any more (if that indicates something to you).
Eventhough things might sound cool I think it is important to consider what they trash as well. Especially if you managed to record something that has really great sonics from the start. You should always remember that neither of these plugs will make your basic audio sound better. They'll both alter the sonics in some degree and your ears might like it. But neither won't ever make the basic audio sound better since you will add an additional DSP calculation to the basic sound.
So to summarize: Use the PSP for grains, use the warmifier for cleans but first work your ass off with the basic mix and make the 200-400 + 2000-3500 Hz region sound separated and clean and then ask yourself if the mix really need any additional warmth. The better mix you have without these plugs, the more dissapointed you will be when you insert them somewhere in your mix.
I do not know if ths was to any worth at all, but look out for the word "warm" when it comes to digital audio.