Not all heads sold as Fluid heads are fluid heads.
But you might not want a true fluid head.
The difference is, true fluid heads actually have a thick oil in a mechanism that restricts or frees the movement of the oil.
The head itself rides on a cushion of lubrication that gives true fluid heads a very smooth operation.
The other type, sometimes sold as a fluid head is a friction head. Typically the cheaper heads, sold as fluid heads are a series of nylon grooves that mesh together, that are lubricated with grease.
The nylon and grease combo creates a fluid like movement that is smooth, but is not a true fluid head.
It still relies on tightening the two nylon plates together to create resistance and the grease gives a smooth feel.
Whats the difference? Why would you want one over the other?
On a true fluid head, the fluid has to flow through an opening as the head moves, up, down, left, right, the fluid has to flow through the hole to allow the head to pan.
Opening the hole, or closing the hole creates easier flow, thus easier movement.
On a fiction head, sold as fluid, tightening the two nylon plates together creates a lubed friction to increase or decrease freedom of movement.
If you close off the hole, the fluid can not transfer, and the head can not move.
If you clamp down the nylon plates tight enough the head can not move.
Nylon plates wear, fluid cartridges don't.
Nylon plates perform similarly in cold and hot conditions, depending on the fluid in the head, fluid heads might not perform the same.
Good, true fluid heads will have a temperature rating, and the rating is basically describing the oils thickening and thinning under temperature.
If you are looking for long term performance, and life span, a true fluid head is the way to go.
It will be smoother under a wider range of loads, and will be smoother when off center loads are put on it.
Most all guys looking to place a spotting scope on top of a tripod will be more than happy with a friction head that is marketed a a "fluid type head", or a " fluid motion head", or whatever marketing scheme the manufacturer uses.
It won't last as long, and it won't perform like a true fluid head, but if its smooth enough for you, do you really care?
A true fluid head is going to cost more.
Its up to you. I would guess that you will be fine with a "fluid like head".
A head like the manfrotto 128RC micro fluid head with quick release is an example.
Its a grooved set of nylon plates with grease.
Its marketed as a "fluid head" but has no fluid cartridge.
Its cheap,($100) and lots of guys like it. But a fluid head it is not.
A good fluid head like a Sachtler will cost you about $600 on the cheap end and much more than that for professional level stuff.
The question is, what do you need? what do you want? and what can you afford?
