I have heard of it. From the other forum's testing of different transmitters.
I have only used the Procaster.
For what it’s worth, the other site rated the Grain above the Procaster.
Spitfire AM transmitter. ...Made in the UK and cost around 90 to 100 usa dollars.
Found the Spitfire Transmitter on Ebay for $79.95. It appears to be fully built and not a kit.
This one also "meets" FCC rules and may be not all that bad. Many more features.
https://www.ebay.com/itm/184784608562?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20220405142716%26meid%3D7e86c9d835ee4af3b37f818a4cbf081f%26pid%3D101506%26rk%3D3%26rkt%3D25%26sd%3D174194447909%26itm%3D184784608562%26pmt%3D0%26noa%3D1%26pg%3D3458402%26algv%3DDefaultOrganicWebWithV11WebTrimmedV3VisualRankerWithKnnV3AndUltBRecall&_trksid=p3458402.c101506.m1851
They're made by the same people, I think.
It's nice to know they're companies still interested in manufacturing part 15 transmitters for AM , considering the band is dying . Fm transmitters are easy to find but few meet usa regulations, though many claim they do .
Here's the UK homesite for these transmitters
Notice that there's a third one called the 'Mosquito' good for 1-Watt and a 4th one called the 'Tornado' 1 to 15 Watts!