What do these Product features" mean?

Product Features
# Paraffin cartridge Is this something good?
# 1/2" NPT female connections do I use teflon tape or some special putty on threads?
# Built-in check valves What's a check valve for?
# Service stops What are service stops for?
# Temperature control only
# GROHE TurboStat Technology
# Separate volume control required
# Requires Twin Ell for shower/tub combinations with diverter tub spout Huh?

On this site are articles on faucets. http://starcraftcustombuilders.com/articleslist.htm This will help you get comfortable with terminology: cartridges, valves, etc.

Product Features
# Paraffin cartridge Is this something good?

It's how many of those are made

# 1/2" NPT female connections do I use Teflon tape or some special putty on threads?

Teflon Tape or thread sealant, I like the Teflon paste pipe dope. (plumbers putty? no way!)

# Built-in check valves What's a check valve for?

Prevent crossover

# Service stops What are service stops for?

Allows replacement of cartridge without shutting off other fixtures.

# Temperature control only
# GROHE TurboStat Technology
# Separate volume control required
# Requires Twin Ell for shower/tub combinations with diverter tub spout Huh?

Does not have a pass through built into the body of the valve, which means you add the shower riser change of direction with a special fitting, or you make it from fittings.

Paraffin operates the thermostat motor because it will respond to temperature changes quickly. Any thread sealant can be used on the connections. Check valves are are not usually necessary, unless this valve is strictly for temperature control and you use "volume controls" to turn the water flow on and off. Service stops are to shut off the water to the valve while working on it. A twin ell is ALWAYS necessary when the valve body does not have "restrictor" device in it. In other words you CANNOT install a pipe from the bottom down to the tub, and another one up out of the top opening to the shower.