I'm new to Step Up Transformers

There are many fine quality tube based phono stages that offer sufficient gain for a LOMC cartridge and do not contain a step up transformer internally. Many of those use a solid state or hybrid gain stage in order to achieve that goal (Manley, probably ARC), but some even do it all with tubes (Atmasphere) and that can be done while preserving a good signal to noise ratio, contrary to what some will say. 

Aesthetix offers all-tube high gain phono stages which I like, but, they have more noise than most tube stages employing only tubes for active amplification.  Among my favorite tube phonostages are those made by Audio Note which require an additional step up transformer, Zanden (built in transformer), and Viva (built in transformer).  

  Thanks for all the responses -  it's great to have access to all the experience out there. 

    My Zestos does have a MC section - it has settings for Low Gain or High Gain. 

My confusion was because a friend with the same phono preamp as mine was telling me a SUT would improve the sound. And others online were saying similar things. 

My Zestos does have a MC section - it has settings for Low Gain or High Gain. 

My confusion was because a friend with the same phono preamp as mine was telling me a SUT would improve the sound. And others online were saying similar things. 

Your Zesto Andros already has SUTs for MC application internally, followed by an internal tube MM phono section. They are Jensen's as used by Lamm, Conrad Johnson, ARC and others.

You would only benefit from using an external SUT if it was higher quality or suits better your cartridge than the internal SUT's in the Zesto. Having installed a Zesto with a variety of top MC's it is a very flexible SUT with multiple loading options. You would have to spend large to get a significant improvement.

The Zesto employs a step up transformer for its MC input.  If you go with a separate step up transformer into the MM input, you will be substituting step up transformers.  Whether you will like an alternative step up transformer is dependent on the quality of the alternative, compatibility with the phono stages, compatibility with your cartridge, and personal preference.

The cost of any alternative step up transformer would also have to factor in the cost of another pair of interconnects.  Some of the better standalone devices can be quite high.  The right choice depends primarily with your chosen cartridge, and some companies even wind them specifically for your cartridge.  If you go that route, you might want to learn a lot more about matching.