(1) The amount of weight you use will determine whether the weight moves fast or slow, but you should always lift with the INTENTION of being explosive. So, if you are lifting really heavy the weight will move slow but you are trying to move it fast.
(2) Yes.
Finally, I would do the shrimp over the SLS, as it is harder.
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In fact, Kelly Baggett, a well known speed coach, has said that he finds mastering BW exercises like the shrimp before or during weighted exercises makes a person gain strength in the weighted exercises faster. So, you could even replace one squat (say friday) with the shrimp.