I have owned 3 of these lenses (and to be fair 3 of the plastic fantastic mk2)
If you are getting one for free / gifted then great, but as with all used lenses please take care to check the following:
1. Mould / Fungus. Hold up to the light, tilt a little to get some of the black interior of the lens behind the glass as well as light passing though the glass, look carefully at everything. There will be dust. If the dust has legs or a web then don't put the lens on any of your kit. Mould and fungus is notoriously easily transferred. If you are dead keen get it cleaned by a reputable repairer. I personally would just bin this particular lens if it had mould (I bought one two weeks ago witht he very beginnings of mould developing, straight back to shop, didn;t even make it onto a body for testing)
2. Focus accuracy. Focus on infinity manually (using the scale) Point the camera to a very distant object. Refocus if required.
Check your shots. Try the same on AF using the centre point. Check your shots. My 2nd copy of this lens died because the focus helix was compromised, probably as a result of a drop.
3. Check the focus ring. Any chips or distortion imply a drop. Calibration could be way out, other unseen damage.
4. Stop the iris down, press the depth of field preview button as you do so, check the stops are uniform, that the blades retain their shape exept wide open, and that there are no oil smears on the blades, as this will affect stop down tine, giving you a lot of over-exposed shots.
There are also a few other things to un-recommend this particular lens:
The AFD focus motor is slow and very noisy. (mk 2 quieter)
MF is gritty and ratchety (mark II not gritty, more loose feeling)
This lens has a cult following, and I am a sucker for it, totally unreasonable. I like the build, as I also love my original 28mm f2.8, but the prices are getting daft (not an issue for you)
There is nothing optically to recommend it over the mk2, same iris shape, same optical formula.
If it's clean and it works right and isn't going to damage your other lenses then great enjoy. Just be very careful before putting in on your body.
In comparison to your 1.4. Well, at 1.4 the 1.4 is the winner. At anything else it's just about even stevens. Except that the 1.4 is quicker and quieter to focus with its USM micro-motor. The f1.4 is also nicer to manually focus.
I wouldn't sell the f1.4 to pimp out an old lens that might die next week.