I have that very ultrasonic cleaner. I bought the largest one Amazon offered. It was about $230. I waited for the price to drop and the seller offered a coupon.
It's works well enough. I have only used it for valve covers so far. I used dawn dish soap. The built in heater is nice but takes a while to get to temp. Just as you described with the solvent tank, soak scrub, repeat, yields the best results. I will add that my stuff was pretty caked with oil so I wasn't expecting parts to look new. Some elbow grease was still required. The longer you leave the parts in the more effective it is.
FYI LS heads do not fit in the 30L completely 😂