Back in the early seventies I owned a Mellotron M400. I ordered mine with Strings, Flutes and Brass. If I had known how bad the brass sounded I would have ordered the Choir sound in place of the brass. The cost of that Mellotron, back then, was nearly $4000. Elektrostudio's Tapeotronic delivers a great all round M400 emulation with full MIDI learn and control of every function, as it should be. It has Strings, Flutes and Choir.
I have tried several free Mellotron emulations such as: Tapeworm, Meltron, Nanotron, Mellosounds, Redtron, etc. Though I had general issues with the sound of a few of them, the main problem was the lack of MIDI control of every one of the handful of controls some of these types of instruments have. Tapeworm doesn't even have a volume knob on it's control panel. And, the 'Octave Mellotron' sound in 'Stringer' is a half step out of tune from the other emulations in the bunch. If a virtual instrument designer is going to put something out there for people to use(free or not) then make it useful.
After plodding through many VST instruments(both free and paid) over the last three years I have changed my order of priorities. Yes, sound is very important. But, I only have two hands and two feet. If I can't control, at the very least, the key parameters and functions of the VSTi from my MIDI keyboard and pedals, then that particular VST instrument is not usable for me. Come on, having to grab for a mouse or the touch pad to move the cursor over to the volume control on the screen of your laptop while you're trying to play is just a NO-GO!!! For accuracy of interface, graphics, overall sound and full remote MIDI control from your keyboard controller, Tapeotronic is the winner for me. In fact, all the instruments in the Elektrostudio Analog 10 Pack are superb. And best of all, they are free! I have no problem paying for a VSTi of good quality, and sometimes you need to pay for the quality of sound you want. However, if you spend enough time searching, you will find some free software that is truly amazing. Download the pack. These instruments are emulations of the most famous keyboards of the 70s & 80s. I am certain you will be quite impressed. The most current Rev is 2.54b. While you're at their website send them a note thanking them for this wonderful gift. My host Software is Cantabile Solo. BTW, I do not work for Elektrostudio. I am just impressed that they made these instruments truly usable so that musicians can make music.