Basic, simple. Solid as a tank: it is run over by Land Rover.
No buttons or unnecessary functions. The key is there on the other hand (a pad, a ground lift)
What manual? There is a pub LIVERT with all Radial products, but I have not seen a manual. Well, for Di, there is not really necessary.
The Sun takes a few more levels than (say) a BSS. The sound is clearer, with a nice attack. On low, it's pretty noticeable. On a guitar just by Mangy cons is not a "too much". The grave is well mastered but lacks a bit of "balls". on the other hand, it's not drooling for a penny.
I did a test with eight different DI with bass and acoustic guitar. The only one that liked best was the Avalon (logical considering the price). The Radial is an excellent value for money. For me, it is a bit above the BSS. Recommend.