The grey oblong head, normally with filter drawer in the head, was designed for an alternative 150 watt bulb. The higher watt bulb would be useful for color printing or very big enlargements. The older back heads are fine with recommended replacement bulbs. Raise the socket to the highest position for added safety.Black round heads need the short neck bulb, the grey oblong can take the common long neck bulb.
I never experience Newton rings with my 1c. The 1c silver slider which raises the condenser can be position so all the condenser's weight is not on the negative. In effect a spacer.
I did experience rings one time with a Valoy. The Valoy condenser rested firmer on the negative. When I figured it out I created a thin shim on the negative carrier. I could also keep the condenser raised slightly but it is not as convenient as on the 1c.
The 1c makes it easy to spot dust on the negative. There is a clear view of the negative when you tilt the head back. The helical vs bellows reduces hiding places for dust. Once the condenser is positioned on the negative there is little opportunity for dust to migrate onto the negative from outside the enlarging head.
I agree. I had a V35 and sold it for the less expensive, smaller 1c.I use the 1c when I want black borders -- it does them perfectly. The glass of the condensor and the Focotar 50 mm f4.5 lens as well as the anti-Newton glass is excellent, and the autofocus is spot-on after I adjusted it according to the instructions. I use the 1c when I want black borders. Print quality between the two enlargers is practically identical.