I've traded at both firms(Echo previously, Assent currently) and can list the tradeoffs to an accurate account.
Assent: The deposit you make at Assent is for "compliance issues" or so they told me but that's only on your initial deposit for a year. My commissions are low and the platform is excellent with exception to the stability in the last couple months. The tech guy is a complete asshole and blames any issues when my platform goes down on "Hoboken." The mentoring/training isn't that great but I'm still learning new things. I like that there are no desk fees or monthly fees except for the NYSE book and esignal which comes to roughly $165 a month. I also get AMEX and NYMEX data feeds for free(spot price of crude, XLE, etc). The people aren't as cool or fun as at Echo. The leverage is relatively small $5k deposit gives you roughly 150-175k bp for prop.
The extra tools like free sub to Trade the News is extremely useful. The office kinda looks like shit but that doesn't bother me too much. Management is okay.
Echo: Their Sterling Trader platform is pretty decent but it's suspect to crashing at high volume moments. I really like their charting but their executions are slower than Anvil's platform. Tech guy is extremely cool and management is professional. The office is really flashy with 42" plasmas everywhere and a spacious trading floor. Monthly fees come to roughly $370 a month(open book included) plus $60 extra if you wanna trade Nasdaq. You have to pay extra for AMEX and NYMEX data feeds(like $15-30 per chart/feed). They are extremely generous with their BP...willing to shell out nearly double or more than what Assent will provide. Coworkers and atmosphere are much more cool here. Free breakfast everyday and free sodas along with a game room. Considering going back to Echo after my 1 year lockup is done.